I also think that this gov't disability has gone on FAR too long and he COULD be getting his life on the right track. I can't believe he's OK with just living in this crappy little apartment for this measly cheque each month. It boggles my mind. He's a smart person and could have had a rewarding career--who knows, maybe it's too late at this point--but he hasn't and doesn't even TRY.
but see, that is your opinion on how someone else SHOULD be living their life. he's 50 and he's "earned" the right to live as he sees fit, to do as much or as little as he chooses. even if you don't approve.
and your mom also has the right to enable him if she chooses. if she wants to buy his groceries and do his laundry, that's her choice. knowing that he certainly won't starve to death, or run out of clean undies.
you have the right to NOT give him a dime if you choose. it's your money. it's no different than a telemarketer or some fly by night non-profit asking you to donate. you get to say no. period.
live and let live.