How to flirt with cousin? Because I met all the requirements and it's still grayed out.
Did you do naughty stuff with them on the train?
There's basically a detailed score but to be real you have to start by
1) not be rude to them after they gloat upon getting the first probe
2) not really confirmed but don't use any underhanded bidding tactics against them for the 2nd probe; sacrifice the platinum for it.
3) prioritize saving them for the 3rd probe and don't treat them like shit.
4) At the high-profile party on Dhaal, locate your cousin, compliment their new look, then encourage them to dance with you.
5) on Dhaal prioritize saving them instead of brokering a deal with whoever the Farrow Facility owner is (determinant). You HAVE to make sure they get released or a weird pathing bug can occur where it narrates that Feruze had to save them later. You'll know you're on the right path if you get an e-mail of gratitude from them and say "May the best Steele win!"
6) Finally, after boarding the Train on Phaedra II, get a real good chat with them, and exhaust all the dialogue, including why they are so adamant about winning, why they seem to not like you, and suggest working together and giving their respective dads the middle finger on what they want for their legacy, cuz it's your lives, not theirs. After all this you should be able to flirt with them and that will open up the relationship with them.
7) following that if you did it right and got kinky with them on the train, you should be able to meet them in the jungle after the train station's exit point and choose to sidle up to them, flirt more, and eventually have sex.