She's your Mom, too, and I think I'd protect my share if at all possible - keep your eye on the cheese. You're entitled to it at this point (until she redoes her legal papers) and I'd do it legally! Call your local bar association and ask for good attorney referrals or check out ratings of probate lawyers (Martindale Hubbel). Save copies of your bros emails, everything - lawyers see this evil every day. If the sibling sees you're not going to cry and run away -- and it's going to get expensive on his end, also, -- maybe he'll play fair. I don't know how legal fees end up being charged but sounds like he's too greedy to want to fight this out - hopefully.
I'd go see her. This greed goes on every day. CPAs/lawyers have a saying something like until the parents die they are 'siblings' and afterward they are 'heirs' and nothing more.
I'm confused - your brother has complete control - does that mean she's bequeathing everything to him? If that's not the case maybe you should go for a guardianship of your mother to protect her and to make sure the cult religion and your brother don't X you out.