Kaeya

diluc but more extreme and for a lot longer. my headcanons flip around a lot, between a nice normal family and kaeya and diluc being crepus' little wives. he ends up the same regardless.
was sexually deviant before he hit puberty, simmering in his thoughts and desires, figuring out whether he was normal or not. (hanging around drunk adults had him overhearing a lot of questionable things the average mondstadt man got up to.)
there's a joke among the seediest of mondstadts residents that varka had to take all the horses away from kaeya for a reason. kaeya laughs along with this and promises to show them an interesting time when they return. is open to being involved in any beastiality but is only really into horses or large dogs topping him.
part of mondstadts kodocon circle along with rosaria and lisa. gets off on little kids calling him their big brother and playing into it. dosn't really get the same reaction from diluc (because of all the walls he's put up), but happily provokes diluc's own incest kink.
typical nights include letting his body be free use to the handsome men of mondsdadt, drinking until he's barely concious and covered in cum and sometimes piss. people know not to cross too far of a line, no injuries or marks above clothes, lest they end up in the ditch.

Flins

does not subscribe to human morals but is also not that kinky. (by comparison) most children do not interest him, and while he may get off to his person of interest watching him be taken by an animal, he does not care about the beast itself.
things like crossdressing or ageplay don't really make sense in his brain, or are of interst. he prefers more tangible things like bondage or taking more then his current form can handle, being literally split as rerir's inhumanly large cock forces through him. or even his polearm, if they're feeling destructive.
although he does have his sense of pride and docorum to live by, so pervasing these that he holds so important is thrilling.
rerir is his current fancy, the taboo betrayal of letting the man who is the enemy of not only him, but his entire sect fuck him over the graves of his companions is too good for flins to pass up.

particularly likes cnc, violence and degradation. he does not bleed and so long as rerir avoids his expensive overclothes he enjoys watching the man cut his dead flesh open, purposely not letting him healing kick in. he also enjoys dominating and breaking his beautiful beast on a leash to mould him into something soft and obidient but rerir need not know about that.

Ororon (+ Capitano)

does not subscribe to a lot of human morals like age of consent or being against beastiality. he is part animal himself, and can comune in some sort of basic language with them. he is however staunchly against rape. he thinks taking advantage of someone, or something is dispicable. his heart's in the right place but he's a little developmentally slow.

into fucking outside and voyerism. ororon will readilly admit it but capitano wont, but they both love to force the other fatui to listen to ororon squeal while he gets pounded. it makes capitano rougher then he would usually be.
capitano is pretty vanilla but likes their size and age difference, how ororon's little waist fits between his two clawed gauntlets. he likes how lovedrunk and stupid he can make ororon from a little playing around and kissing, ororon drooling on himself and babbling to capitano like he isn't a full grown man.

ororon is also into painplay, choking, cutting, hitting etc but capitano will rarely indulge him how he wants.