Senior citizen law

My mother and married brother stay in Chandigarh for last 40 years. My brother married 15 years back. My mom was stating with them. My mom is quite submissive and now retired from govt job. My sister in law has been troubling my mom ever since they are married. Starting from exploiting her for money, forcing her to do all house work, mentally harassing and torturing her by ill treating even in front of neighbours, not letting her talk to others on phone as per her willand what not. It all happens when my brother is not at home. More so few instances which happened in front of him were ignored thinking as small tiffs. Now it has reached to physical abuse where my mom was hit. We are financially not too well off and my brother stayed quiet as everyone wanted things to be resolved within house boundaries. I as daughter also was never informed in last 15 yrs until neighbours called me to save my mom. My mom is now with me and we are trying to have two houses so that mom can stay near and still not in same house. She is mentally very disturbed, has completely lost eye sight in one eye due to glucoma and now undergoing treatment for other. She has already threatened my brother that she will take one house which is built by my mom and my late father whole life savings. Pls suggest legally what can we do to ensure she cannot force my mom. Can my brother file divorce without her consent!?