This is a dilemma, don't you just hate that word ,it seems to me that you and your Dad have to find somewhere nearby for your brother to live ,its not good for either of them to live with this constant stress,.Start with the Doctor ask if there is any way your brother can be helped.maybe a visit from a social worker, skilled in these matters .Its obvious the two need to have their own space there possibly could be some financial aid to get your brother a small place of his own .The fact the police have been involved and physical abuse shows it has gone far enough. Good you are concerned for them both and its really tough on you aswell.Good Luck let us know what you decide , my ultimate opinion is ..split them up ,at least living together .