I'm sorry if I didn't catch this previously, but is there any way that you can avoid your sister? Or if she goes into a rage, tell her to "take a time out" and rather than argue/fight, state her behavior is unacceptable so won't be responded to (ignore her). I can't help but wonder if she needs some psychiatric medications. Maybe some antipsychotic, plus anger management classes.

I wouldn't say that my brother is quite to the degree of your sister, but he is very prone to extreme anger outbursts when anyone says something he disagrees with (especially if it is political). I've simply had to leave the premises those times and take a break from him. Sadly, he is not the type to ever apologize, but as I'm very good at letting people's offenses go, if the next time I see him he is calm and civil, I just do. My brother should really be in therapy and likely take medications. My sister agrees. But it can be hard. He lives alone, so by not having people with him a lot he just persists with that behavior. He is very lonely, but that's not quite enough yet to convince him to get the help.

I so feel for you that you have a very unwell dependent brother and an ailing scared mom. I know it is hard to know what's best to do or it can be frustrating when people won't take steps to make things easier for all. A few years ago, my family was in a similar situation with my dad whose behavior became reckless and he ended up in the ICU for over a week. It was sad that it ended in such a way. He has been in assisted living since. It is a relief, though. My siblings and I had to be tough in demanding he get help.

I know alcohol is not involved in your family's case, but I'll share that in Al-Anon, it is very emphasized that family members MUST take care of themselves first. Too often family members enable their loved ones with addiction. It becomes hard for any progress to take place. Ideally it is helpful for an intervention to happen, but if that's not possible (i.e. if all family members are in some form of crisis), stepping away may be needed. Yes, that sometimes causes resentment, but it can be for the best. It's not up to you to "save" your family IF they have no desire/intention of working with you to make positive changes.