Like, commit to it if you're gonna do it and not suddenly reveal that one of them has been adopted!

I find that adopted thing interesting in a baffling way, because the only forbidden aspect it really removes the genetical similarity, which really only matters if the characters are going to have children. All the power dynamics etc. will stay intact, which makes it feel even more of a cop-out to me. Like it's a cop-out that doesn't even bother to actually cop out much anything.