It’s traditional, to lose one son to the whims of the other.
The story culminates in the father, alone, making an impossible choice. He sacrifices his gentler son. The family is destroyed. The Imperium prospers.
But this real and sordid affair will not end in one big decision. To surrender Gregor, Aral should quietly have Vordrozda removed. He should lie, and keep lying, and gradually twist Gregor into a sullen and obedient thing. To surrender Miles, he should only continue doing nothing until the very end.
Aral is so tired. Cordelia decides: for now, they wait, and watch what happens.