Hi . . .it is a difficult situation . . . I am not a med professional so I will speak from an individual perspective . . .
To me, your brother needs more help than either you or your Mom can provide. If his behaviour is as you describe it, then he is potentially a threat to you and anyone else in the house. I would suggest, and these are only suggestions, that you consider the following:
1. contacting your own doctor and explaining the situation to find out what the options are -- this is a health concern for you because of your own GAD;
2. depending on what your doctor advises, contact your police force, explain the situation, and ask them what their protocols are;
3. consider getting a lock for your bedroom door --- for me, with anxiety, the worst thing are "surprises" . . . . and especially if I am asleep; and,
4. remember that as much as you may want to help your brother and keep him out of an institution, you have to consider your health also . . . your brother does not seem to be responding appropriately to the meds + outptient care and probably is not able to make informed choices right now and perhaps intensive inpatient care might be a difficult choice, but it may be the best one before his behaviour escalates . . .withdrawal, at the best of times, is difficult but coupled with derression, bipolar, and anxiety, it does need professional intervention . . .
Please let us know how you and your Mom are doing when you can . . .take care, kc