Harassment for dowry

My sister is deaf and dumb so she cannot talk properly before 1 year she got married. Before marriage they have not asked dowry but than also we have given gold as per our family's status. After marriage 2 months my sister had no problem they have kept nicely after 2 months her mother in law one day asking extra gold and they have started torturing my sister her husband started beating her. He did not allowed her to talk to us. After 9 months she is pregnant. That time also he tortured like a slave but with all the neighbours they have acted like they keeping my sister like princess. One day we got a call from my sister that please come any one to pick me as my husband allowed me to stay in my parents house for some days as she is suffering from morning sickness due to pregnancy so she came here. Than only we came to know that her husband tortured her than after 1 month her husband came here and asked sorry to her and took her back. Than after 5 days again problem started and he started beating her and called us and scolded badly and started fighting with us so we went her house and we tried to solve the problem but they are not ready so we took our sister with us now pls help me what shall we do legally for my sister future