Adopted children are step-family (well duh), therefore still incest according to patreon's guidelines.
I'm not from the US, so I don't know the statutes, I was just going by what other dev's seem to have gotten away with. Also see comment from someone above regarding New Jersey, apparently. Regardless, roommates is a good option as I'm sure someone would do an incest mod for those who want it, if it is anything less than full incest.