possible elderly financial abuse?

location: lake isabella, ca
my grandma (70) & my little brother (19) have lived together for almost two years. she took him under his wing and let him move in with her and her then husband to help my brother get back on track. things went poorly and my grandma and her husband got a divorce. since then, she has been struggling very badly with money. she gets social security checks and food stamps and is not getting what she needs to keep them afloat.

my grandma can’t work, she’s getting old and her body doesn’t allow her to stand for 8+ hrs a day. therefore my brother needs to work, but he doesn’t. at first he was using the excuse “i don’t have my birth certificate,” but he does now. now it’s “there’s no jobs up here.” which could be true, however there’s always SOMETHING. dogsit, mow lawns, ANYTHING! he just doesn’t want to.

my grandma recognizes his behavior and just defends him, but i genuinely think it’s because she’s scared of him. a couple months back he got arrested for punching holes in the walls, leaving marks on her, etc. he listens to her conversations and has gone through her phone before (weird stuff, i know.)

not only is he violent, his lack of drive is making my grandma stress about money. she recently opened up a credit card just to pay her bills. she’s never had a credit card in her life. i’ve told her it’s not a good idea because won’t be able to pay it back, but she’s not listening to me. she has to pay for everything INCLUDING my brother’s weed habit.

i’m unsure of how to help my grandmother. she won’t kick him out, she won’t tell him off, won’t set boundaries. he is going to genuinely drive her into the ground financially. i’ve tried helping her by sending her whatever money she needs to finish paying her bills, but then it’s “your brother needs his weed, can you send $100.” it’s annoying. and i feel trapped because if i say anything to him, he will take it out on her.

what would you guys do in this situation? how can my grandma be helped financially/legally?