@Aldistar,
I agree, and with all the others. Things are just getting worse, not better, and your husband knows it's her, not you.
Change your locks. Don't move in with your mother-in-law - she's obviously not supporting you. The thing is, it doesn't matter WHY your sister-in-law is doing it, everybody is just pretending it's not happening or that you should overlook it.
Get a backbone and tell her to stop it, right now! Tell her you will go to the police. And tell your husband you demand his support. His relationship with his brother has already withstood the stuff his wife has done. It will withstand whatever you decide to do.