1. Family relationships
Chinese are very conscious of familial relationships. There are specific words for specific relationships, often making a clear distinction between maternal and paternal side family members, and making clear whether that person is older or younger in a relationship. A person of a younger generation would not, unless they are being deliberately rude, call anyone of an older generation directly by name. Generally, a (respectful) younger person of the same generation would also avoid calling an older sibling or cousin by name, but instead would reference the relationship.
Father: 父亲 (fuqin) [author’s note: this, right here, is what made me put in the note about how q is pronounced. T_T;;;]
Also used: 爹 (die) This is less formal, more colloquial, more like “dad.”
Also used: 阿爹 (adie) This is even less formal, more like “daddy.”
Example: Wen Yuan calls Lan Wangji 阿爹 while crying, at their first meeting.
Note, this is in the context of historical China; in modern times, 爹 is not used. Using 爹 to refer to your father would be considered very old fashioned.
Mother: 母亲 (muqin)
Also used: 娘 (niang) As with 爹 (die), it’s less formal, more like “mom.” Old fashioned, not used in modern parlance.
Older brother: 哥哥 (gege)
Also used: 兄長 (xiongzhang), which is a more respectful way of saying older brother.
Example: used by Lan Wangji when referring to or addressing Lan Xichen.
Older sister: 姐姐 (jiejie)
Also used: 阿姐 (ajie): a more familiar way of saying older sister. Example: used by Jiang Wanyin when referring to Jiang Yanli.
Younger brother: 弟弟 (didi)
Younger sister: 妹妹 (meimei)
Uncle, paternal side, younger brother to the referring person’s father: 叔父 (shufu) Formal, respectful.
Example: in the Xuanwu cave, Wei Wuxian uses the term “your shufu” when he asks about Lan Wangji’s uncle, Lan Qiren. He doesn’t use Lan Qiren’s name.
Also: 叔叔 (shushu), slightly less formal.
Note that 叔叔 (shushu) can also be used to refer to a male of the referring person’s parents’ generation, who is younger than the parents. Typically the person would reference “[family name] 叔叔” to indicate a respectful but close relationship with that person. Example: Wei Wuxian refers to Jiang Fengmian as 江叔叔 (Jiang-shushu) or “Uncle Jiang.”
Uncle, paternal side, older brother to the referring person’s father: 伯父 (bofu) Formal, respectful. Also, 伯伯 (bobo), which is slightly less formal.
Note: similar to 叔叔, “[family name] 伯伯” would refer to a male of the referring person’s parents’ generation, who is older than the parents.
Uncle, paternal side, who is the youngest sibling of the referring person’s father: 小叔 (xiaoshu). Literally, “little uncle.”
Example: this is how Jin Ling refers to Jin Guangyao, since he is the youngest sibling of Jin Zixuan. Note: this demonstrates that Jin Ling doesn’t recognize Mo Xuanyu as his uncle. If he did, Jin Guanyao would be “second paternal uncle” or 二叔 (ershu) and Mo Xuanyu would be the little uncle. Instead, Jin Ling basically just calls him “you” directly.
Uncle, maternal side: 舅舅 (jiujiu). Example: this is how Jin Ling refers to Jiang Wanyin.
Grandmother, maternal side: 婆婆 (popo)
Note: can also be used as a general reference to an elderly woman. Example: Wei Wuxian refers to Wen Yuan’s grandmother as 婆婆 .
2. Sect relationships
Persons admitted to a sect are considered similar to family, and have relationships that are referenced similar to family relationships. The person’s assigned “generation” is determined based on who their master is, and the order in which they are admitted to the sect, not by age. Therefore, because Xiao Xingchen’s master was the master of Wei Wuxian’s mother, Xiao Xingchen is Wei Wuxian’s sect uncle (shishu), even though he’s younger than Wei Wuxian. As another example, Wei Wuxian is referenced as the “oldest” sect brother in Yunmeng Jiang Sect, but he could have sect siblings who are older than him in age, but have been disciples for a shorter period of time. (Possibly, he and Jiang Wanyin both started training/ became disciples at the same time, but because he was older than Jiang Wanyin, he was referred to as the older sect brother.)
Chief Cultivator: 仙督 (xiandu). The word 仙 means immortal, but in context refers to the cultivation world (i.e., the cultivation sects). The word 督 can be translated as overseer or governor.
Sect leader: 宗主 (zongzhu) The leader of a cultivation sect (in the xianxia fiction genre) or the leader of a martial sect (in the wuxia fiction genre). The members of the sect would refer to their own sect leader as 宗主. Persons outside of the sect would refer to a sect’s leader as “[family name] 宗主.” Example: Sect Leader Jiang, Sect Leader Lan, etc.
Master: 师父 (shifu) This is a person who has agreed to accept disciples to pass on their martial (or cultivation) knowledge. Example: Baoshan Sanren is referred to as Xiao Xingchen’s shifu rather than sect leader, since she did not establish a sect.
Wife of the master: 师母 (shimu) This is a gendered term, but I put it here as an example of what a disciple of Lan Wangji might call Wei Wuxian in fanfic as an affectionate/ teasing term. Note that if Wei Wuxian had a better relationship with Yu Ziyuan, this might be a term he could respectfully call her, since he was a disciple of Jiang Fengmian.
Sect sister, older (i.e.. earlier-admitted): 师姐 (shijie) This is how Wei Wuxian refers to Jiang Yanli.
Sect sister, younger (i.e., later-admitted): 师妹 (shimei)
Sect brother, older: 师兄 (shixiong). Wei Wuxian is the “大师兄 (da shixiong)” meaning the oldest sect brother in ranking. Anyone above the referring person in ranking would be referred to as 师兄 (shixiong), though they might also specify [number]师兄 to refer to their particular ranking in the sect.
Sect brother, younger: 师弟 (shidi) Any male lower in the sect’s ranking can be referred to as shidi, though they may specify the ranking number to refer to a particular sect brother.
Example: the sixth shidi (六师弟) of Yunmeng Jiang was captured by the Wens for shooting the one-eyed monster kite.
Sect uncle, younger: 师叔 (shishu) and sect uncle, older: 师伯 (shibo). Refers to a person who has the same master as a parent of the referring person. Example: Xiao Xingchen is Wei Wuxian’s shishu because he shared a master with Wei Wuxian’s mother and was admitted as a disciple after her.
Note: canon isn't explicit on how sect siblings are numbered, but typically if there is a huge number of siblings in a family, the brothers are numbered 1 to x and the sisters are numbered 1 to x based on age, so the ranking number would be static, and whether you would call someone a [number]-xiong (ge in an actual family) or [number]-di depends on the referring person.
In the Jiang Sect, Wei Wuxian is 大师兄 (da-shixiong) to everyone as the first ranked disciple. Jiang Wanyin would be 二师弟 (er-shidi) (second younger sect brother) to Wei Wuxian, but 二师兄 (er-shixiong) (second older sect brother) to everyone else. So we assume the one in the novel who said that Sixth Shidi was captured by the Wens is someone ranked #3-5, since he called #6 shidi. If it was a younger disciple, he would have said Sixth Shixiong. The very youngest disciple could be called 小师弟 (xiao-shidi) (little sect brother), but would be referred to by number if a newer disciple were admitted.
The female sect disciples would be similarly numbered. If a sect brother referred to a sect sister, he would call her [number]-shijie or [number]-shimei based on whether they were admitted before or after him.
Keep in mind that the Jiang Sect is the only one that had a direct reference to a numbering system, and they're a small sect compared to the others. I imagine if you get up to the large number of disciples you see in Gusu Lan or Lanling Jin, it doesn't make sense to say "ninety-fifth shixiong" but instead just call them shixiong or shidi without numbering them.
3. Friends and acquaintances
Bro: [family name]兄 (xiong) Friendly way of referring to a male friend of the same generation. Example: Wei Wuxian calls Nie Huaisang “Nie-xiong”
Note: this is really difficult to translate since there’s no real equivalent. I’ve seen translations as “brother” such as “brother Wei,” but it’s a little awkward in English. May be best to transliterate as [family name]-xiong or just use the person’s full name.
(Sworn) older Brother: 哥 (ge) Sworn brothers in Chinese lore undertake a ritual ceremony to pledge loyalty to each other. The younger brother would typically refer to the older one(s) as 大哥 (da ge) for the oldest brother, and [number] 哥 for subsequent ones. The older ones may use a diminutive to refer to a younger sworn brother. Example: Jin Guanyao and Lan Xichen both called Nie Mingjue 大哥 (da ge), but Lan Xichen referred to Jin Guangyao as a-Yao.
Typically the close siblings of a sworn brother would refer to the other members of the brotherhood as family. Example: Nie Huasang called Jin Guanyao third older brother.
Close older male friend: 哥哥(gege) This is used informally, and often styled as [family name or personal name]哥哥. An example might be if two sets of parents are close, they might tell a younger child to call the older friend [personal name]-gege. It can be used flirtatiously, depending on tone of voice. Example: Early in their acquaintance, Wei Wuxian calls Lan Wangji “Lan Er-gege” (meaning the second Lan brother) - he uses it to indicate a level of familiarity/ closeness that is at that point still rejected by Lan Wangji (at least outwardly). Another example: In the Untamed, Wei Wuxian takes advantage of Lan Wangji’s drunkenness to get him to call Wei Wuxian Wei-gege. In Chinese, this puts Lan Wangji in a lower position as the “younger” person.
LIttle: 小 (xiao) An affectionate diminutive that means “little.” I haven’t noticed a canon use yet, but if you’re writing fanfic and want a way for someone older to refer to someone younger, you could use xiao-[family name] for a casual, familiar reference, or, more affectionately, xiao-[one character from personal name].
Old: 老 (lao) A prefix to indicate someone older, usually styled as lao-[family name]. Used informally and familiarly. An example might be someone saying “lao-Zhang from down the street noticed a bunch of fierce corpses by the lake.”
Prefix to indicate diminutive: 阿 (a) An affectionate diminutive that is placed in front of one character from the person’s personal name. Used in informal situations. Example: Wen Yuan is referred to as a-Yuan by Wei Wuxian.
It can also be a diminutive that is used in front of a person’s family name, and used to indicate someone from a lower class/ a servant. Example: the servant in the Mo family that died was called a-Tong. Likely Tong was his family name.
Madam/ Mrs.: 夫人 (furen) A formal way to refer to a married woman. Typically it’s styled as: “[family name of husband]-furen.” It was particularly noted that Madam Yu was referred to as Yu-furen (using her maiden family name) and not Jiang-furen (using her husband’s family name).
Note that Wei Wuxian addressed Yu Ziyuan formally as Madam Yu, not as shimu (his master’s wife) or Aunt Jiang.
Miss/ Maiden: 姑娘 (guniang) A formal/ polite way to refer to an unmarried woman or young lady. Typically styled as “[family name]-guniang.” Example: Jin Zixuan called Jiang Yanli Jiang-guniang. This was why there was such a reaction to Wei Wuxian calling Mianmian by her nickname.
Young master: 公子 (gongzi) A formal/ polite way of referring to a gentleman (son of a good family). Example: Wen Ning refers to Wei Wuxian as Wei-gongzi.
Taoist master: 道长 (daozhang) A respectful way of referring to a priest of Taoism. Example: a-Qing referred to Xiao Xingchen as daozhang.
Senior: 前辈 (qianbei) An honorific referring to someone older. Literal translation is “of an earlier generation.” Usually used to indicate respect for someone of greater experience. Example: The Lan junior disciples refer to Wei Wuxian as Senior Mo or Mo-qianbei after he saves them. When they first met, they referred to him as Mo-gongzi.
In terms of writing in English, as a writer you’ll have to decide what works best for your style. I have my own preferences for titles or diminutives: if it’s transliterated, my preference is using no capital letters and a hyphen (or italicized if not using a hyphen). E.g. Jiang-shushu, a-Qing, xiao-Shu, Wei-gongzi, Nie-xiong. I prefer not capitalizing because it distinguishes from proper names, especially when someone uses “Xiao,” which is a family name in Chinese. For titles that translate easily, you might just use the English version, such as Uncle Jiang, Sect Leader Lan, young master Wei, Madam Yu, or Miss Jiang. For titles that don’t translate easily but that refer to a specific person, you might use the transliteration with a capitalized first letter, such as Shijie when Wei Wuxian refers to Jiang Yanli.