i never really specified if rhett's parents had any biological children, but i imagined they couldn't have children and just fostered and adopted a whole slew who came and went for like 20 years or something crazy like that. so if her mother or father was one of those foster or fellow adoptee kids, he could be her adoptive/foster uncle who's just kept up a good relationship with her parents and her. and then kang could be a cousin through rhett's parents... let's just say for example's sake, rhett's father and nate's grandfather are siblings, so rhett is like a second cousin once removed and charlie would be his second cousin or something.... idk, it's super complex, but it could be a through marriage kind of thing, too. like, a girl i knew had my same birthday and her aunt was my aunt-in-law, so we were related through marriage. our families never spent any time together, but we shared an aunt. soooo something like that?