If your brother starts acting threatening or violent, I'd call 911. I've been in the situation where I've had to protect my grandparents from my mother's actions. We tried to calm her on our own, but in the end, we had to call the police to have her forceable removed from my grandparents' home. I know that sounds harsh, but the safety for your family is the highest priority. Does he have keys to her house? If so, the locks should probably be changed. It sounds like your mom needs to make sure that she secures her valuables. Where is he getting money for his drug habit?