Apparently Stiles isn't their first rodeo. There have been other pliable humans, or wolves, or kanima or whatever, but it's been ages since Laura's been able to persuade Derek to let go enough to have fun. Or 'real fun' as she terms it.
"When he holds back who he is, he doesn't do himself any favours, Stiles." She leans in closer and all he can feel is her warm breath against his ear and her fingers edging steadily further inside of him. "Plus it's not a hardship, right? The thought of my brother taking you doggy-style gets you pretty hot."
Stiles likes that they're on that level of sharing and caring now. That nobody pretends he isn't into the idea of Derek the giant wolf, or that Derek isn't into the idea of fucking him like that, or that Laura isn't into both of them at once. They dirty-talk and they talk shit and finally they end up at the center of a big horny storm that only ends in orgasms, slap fights, and difficult to explain bruises.
Laura likes Derek knotted inside her cunt while Stiles slides into her ass from behind. Every time he moves her body gets jerked around the knot and she moans. If she thinks he's not going fast enough she reaches back to pull him in, her nails leaving scratches on his skin. She and Derek try and stare each other out like the most competitive pleasure game Stiles has ever seen. If Derek breaks eye contact first, Laura squeezes internally, grabs his chin, and makes him face her again. If Laura cracks, Derek smirks and rolls his hips up sharp, shifting the knot further in while he twists a nipple.
Stiles like Derek's wolf dick pounding his asshole while Laura makes him eat her out. She gets so wet and hot that it feels like he's drowning as she fists hands in his hair, dragging him where she wants. Derek shifts and takes that long pink dick of his and forces it into Stiles until he's spluttering and twitching. Then with a growl he starts pumping, claws grasping at Stiles' sides, teeth digging into his neck.
Derek likes them both sucking his dick at the same time, then so many fingers inside him that he starts to arch. When they want to make him beg they suck open mouthed at opposites sides of his cock until he starts trying to hold onto flat surfaces and chairs. The one time Stiles gets his tongue in-between all their fingers up his ass, Derek comes so hard he doesn't speak for ten minutes, just gasps and shivers.
The rest of the time the two of them just hog all the couch space, argue about who should do the taxes, and eat too much take-out. Stiles steals their pancakes, fills their DVR with reality shows, and demands a greater range of condiments.
Apparently they're one of the most effective supernatural issues teams the FBI has ever had the pleasure of employing.