My first question when I read this is “Where are the fathers?” You are a wonderful, caring older sister ,but you need some help from the other adults in the family if this situation is to change. You can’t repair what’s going on at home on your own. So where are the fathers? Do they understand what is happening to their children? Your mother’s behavior is inexcusable and can damage the kids emotionally for a long, long time. The dads need to make it clear that she can’t keep it up and they need to get your mom whatever help she needs to manage her emotions and to learn how to be a mother.
If the men have dropped out of the picture, how about other relatives? Is there anyone you are close enough to that you can have a heart to heart about what is really happening at home? Yes, I know. No one likes to have their cover blown. Your mother will be furious if you start letting other people know how bad it is. But you have an escape route in that you’re going to college. The younger ones are stuck there. Maybe it’s worth being “disowned” if the kids get the help they need. Think about it.
I wish you well.