1) If he's beating your sisters, which as your brother-in-law would mean he's beating his wife, your best bet for getting him to stop is call the police. If your other sister is under the age of 18, you may even be able to call social services or whatever equivalent you have available.
2) If you don't live with the sister who's married to this guy, talk to your family about not letting him be around anyone other than his wife. She, at least on some level, tolerates the guy so she can be the one to spend time with him.
3) If you attacked him, you'd wind up making matters worse for everyone.
4) At the age of 16, in most states you can legally divorce your family and live on your own. If you need to, take this step. It's better to live alone than live with hostility.
5) If he threatens you or actually attacks you, aside from the criminal charges those acts bring, you can get a restraining or personal protection order. While a court order won't stop a fist, it adds a layer of security to you and your family.
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"I know only of one duty, and that is to love."
- Albert Camus
"The creative mind plays with the object it loves."
- Carl Jung |