Can I (US Citi) adopt my sibbling (Student Visa- US) who is 23


Registered Users (C)
Family migration?
Dude becomes a USC, parents in the US on a b2 and i485s, sis on a f1 and wants to adopt.

I've heard of queries for adopting nieces or nephews into the US, 'adopting' a sibling is a new one.