Dowry and mental Harassment

My sister got married 3 years ago now she has to 2 childrens ,recently she given birth to a baby while she was pregnant my brother in law started tourchring her for dowry as well physically and mentally at that time my parent involved to solve the issue he asked a legal notice that my parent should not to see my sister then he will stop harrashing her so in presence of an advocate my parent has signed on a note which states that my parent will not go to my sisters house and he will not come to imy parents home.....and after that he disconnected every information of my sister ...and started harassing her with his words like this kid to whom she will going to give birth that's not mine, and i will marry another lady you and your children should die then only my problems get solved this way he had done.. before birth of a baby he required some amount for that he started making relation with our family again he has took money from my parents. And he not even informed that she got delivered a baby , after few day she got infection in womb for lack of rest and work for that reason she not even stand properly so he came to my parent to care of my sister and said forget about previous legal note.I want to be nice with you ,and at the time of treatment in hospital he started demanding for money for his needs when my parents refused to give money he started saying that I will take her home ,we are refused him to take back and force fully we are kept my sister in my hospital and continued her treatment ,after her recovery we sent to his home after a week he again started beating my sister and the baby child too .so she has protected by neighbors and she came back to my home ,,so I need your help sir how to proceed legally for my sister she wants protection for her children too he will not stop harrasung her and he is two faced man that he is showing off in front of people that he can't leave without his wife ,and he will die without her ...sir please suggest us to how to proceed in legal way