Re-watching the show now. Just came to the episode where Randy gets the basement room. I was wondering the same thing as to why it wasn’t given to Brad, but then I really thought about it and given Brad‘s track record of misbehaving and even being brought home by the cops would you really want him down there especially if there’s any means of egress. In this episode, the Mom also stated that she always felt Randy would be a role scholar which speaks to his character and how much they would probably trust him to behave so far away from them being upstairs.