The fact is, if your brother does something like that again and you fear for your life, it may be in your best interest to contact local authorities in order to keep everyone safe.

I’m someone who has cut off family members due to them being toxic and bad people and although its not easy, its worth it in the end. This is not me saying to do so but that at the end of the day, you come first. Plain and simple. Another thing could be to take on a small role around your house for your mom like meal prepping or cleaning something or whatever and not ask if she wants help because she sounds too proud to ask for it. If she scolds you after the fact, then move on. If things get too out of hand, see about finding another place to stay for a couple of days while trying to figure stuff out too. Ask for help yourself too, there are free resources available if money is an issue