Justice against domestic violence.

Dear Experts, My sister husband is a government employee in Maulana azad national Urdu university - Hyderabad. Whereas we are staying near to Chennai. My sister is facing domestic violence and harassment at their mother in law house. She is having 2 years old baby with her. From last four years (from first month after the marriage) they are harassing my sister and even not providing food to her when she was pregnant and had a small kid of 3 months. They are creating the environment like that my sister would like to leave her husband on her own (to escape from their harassment). They applied the same formula on their elder son’s (Who is also an employee at MANUU) first wife and second wife also. Their elder son’s first wife went away for permanently from his life by getting mentally disturbed. We come to know this issue, only after our sister marriage. My parents and family members had tried to solve the issue in a soft manner just by discussion and they were not changed .They are creating a new stories and blaming my sister and my family members. Recently my sister's mother in law, brother in law, husband and sister in laws were attempted a homicide on her. God grace she was safe from their master plan (she come out from room, started shouting in town ship). Her sister in laws were done manhandling so many time on my sister. Now, I am very much tense that they will harm my sister without doubt. By respecting my parent’s word, we are silent and in patience from last four years. It seems they will not became human beings, even though we will wait for some more time. Can someone kindly suggest me the following? 1) How to proceed legally to get the justice to my sister and her child? 2) On what basis can I register the case? (so that their bail is ineffective , they will be arrested) Waiting for your valuable suggestions.