Here's a plan. See if it works for you.
1) The semester will be done soon.
Talk to your school about taking some time off. Explain the situation to them. They have heard it all before, times 20, and will not be shocked and should not be judgmental. They will, I am sure, grant a request for a leave of absence but you should do it soon before finals get in the way. It's also a courtesy to the school -- they would need to fill your seat for a semester or year or however long you'd be off so the earlier you tell them, the better.
Also, talk to school about things like living on campus (if that's possible) and work/study. Sure, you might be flipping burgers in the cafeteria or filing books in the library, but it's all good, honest work. Another idea is asking about part-time school. Surely you are not the only person who's needed to work in order to afford school. Also ask about aid. Loans, grants, scholarships, whatever they've got. Some might come if you apply, some if you write some sort of an essay. Find out. No reason not to ask.
2)
Contact your folks. Explain the situation. Your parents love you and want the best for you. While they are dealing with your brother and his problems, they will, I am sure, do what they can for you. It's not just about money, it's not just about a place to stay, it's also about support. So tell them.
3)
Contact social services. Again, they have heard this before, times 20. They will be neither shocked nor judgmental. You are in school, your assets are few and your income is not high, but since you are in school and bettering yourself already you may be eligible for more aid than most. But you have to ask. I know, it's hard, because you want to be independent, but this is a matter of getting food on the table and having a table to put food on.
4)
Assess your financial situation objectively. (you don't need to answer these questions online, but you should know the answers)
How much $$ is in your individual account?
What's half of the joint account?
What is your salary?
What are your expenses? And by expenses I mean necessities only.
What are your debts?
Is there anything you can sell? You might have stock certificates, antique jewelry, a car that you could sell down, that sort of thing.
5)
Do what you can to help your financial situation. Contact your credit card companies, if any. If you have debt, explain the situation. Yet again, they will not be shocked. Work out a payment plan if you have debts. Creditors want cash but are willing to take less if it means they will get something.
Contact the bank. Are you in debt? Again, tell them what's going on. See what they can do to help you. Even if you don't have loans with them, it's possible that you'd have trouble paying, say, a monthly checking account fee. Find out what they can do for you. If you've been a loyal customer for at least a year, banks tend to be very accommodating and willing to help figure out how to make it possible for you to keep your account(s).
6)
Contact Al-Anon. Drinking affects the whole family. The fact that folks out of their teen years are playing drinking games says a lot. I am not saying that you, personally, are an alcoholic or even that he is, but it is troubling that drinking led to violence, and it is also troubling that drinking was the centerpiece of a social gathering. Find out what they can do for you -- it's a lot.
7)
Talk to your friends. Perhaps someone has a couch, a few bucks, a lawyer who'll work for a small fee, or just a sympathetic ear. Your friends want to help you. I suspect that they have been watching what's going on, and are just unsure of what to do.
8)
Contact Legal Aid. They're in the phone book. They can help you with a separation and a divorce, and a maintenance agreement. In a divorce, in most states, the party who is most disadvantaged (that's you) can get support from the other party. This is usually true regardless of fault, but this, of course, depends on the state you're in. You need not go hungry by leaving this guy.
9) If all else fails, or it's an emergency,
contact a local women's shelter. They're in the phone book. In fact, even if the situation is not dire, you can always just keep their number handy. Just in case.
10)
Take a deep breath. It's a lot, I know, the process of lining up all your ducks can be hard. But once it's done, it's very fulfilling.
It's good to not be a victim.
It's good to be in charge.
It's good to be the one calling the shots.
It's good to get your life back.
You can do it. I have every confidence in you.