There is hope for you and your brother. From your description, while I don't ever like to give up on another soul, your mam is an adult and makes her own decisions about her life. Unfortunately, there is nothing you can do about her decisions. If she should decide to change, then you may be in a position to help her. If not? Then this is how she will be.
The only person you can change in this world is you, and therein lies your hope. I would wish for you to be able to move away from all the emotional destruction and check into whether or not there is an AlAnon chapter near you. If you can get away from the destruction (you and your brother) then perhaps things may start to seem more sane for you.
If that is not an option, I would suggest lying low and being small and quiet until you get back to school - then seeking out a school therapist/counselor/mental health person (if you have one) and talking to them.
There is most definitely hope for you and your brother. Like your mam though, you'll need to make a decision to seek out help and follow through with it.
I feel for you very deeply. The day I moved away from home was simultaneously the most frightening and most liberating day of my life.