Domestic Harrasment

My sister got married 5 years ago. My sister and brother-in-law both are in private jobs and my sister is getting paid better than her husband. After 1 year of their marriage my brother-in-law started mentally harassing my sister. He started  demanding money from her to give to his relatives and friends. He even made her to pay for the house rent and all day to day house expenses. If she refuse to give the money he used to verbally abuse her,threaten her,point finger on her character,creat all kind disturbance in house,tell everyone that she is very bad, etc etc. My sister tolrated all the harrassment and tried to cover up everything till recently.She even didn't  tell anything to her mother for around 4.5 years.When it became intolerable for her,she decided to live separately. Now she is not willing to live with her husband.As per my sister he is physco type and can do anything to her anytime. We tried to call my brother-in-law elder brother(since his father is not alive and mother is not in good health) and his uncle so that both families can sit together and try to understand ill behaviour of him towards my sister and to solve the problem between them. But his brother refused to come for the discussion. Now we are thinking what to do next. Please guide.