Huge hugs to you. It sounds horrible. I have a partner with an AS and get strength from these boards to focus on my own life and to keep a healthy distance from the problems which AS causes. It is the only healthy way to deal with the situation.
Whatever you say and whatever advice you give your mother and brother will be ignored as neither of them want to change the situation. They have to work it out for themselves and that doesn't look as if it will happen any time soon. Unfortunately, you have to find a way of accepting this and start to focus on your own life.
It is not easy to watch someone completely mess up their life, I know. One thing I have learned is that addicts will suck the life/money/time/kindness out of somebody for as long as they can get away with it. They are experts at finding a weak spot in somebody and will use and abuse it for as long as they are able to.
Stay strong, don't get involved with any of the drama and focus on YOUR life.
Congratulations on your pregnancy!