Female 3 Yrs Child Custody

Dear Respected, Greetings !! I am Grace from Bangalore , Here i have a question regarding child custody , My sister is married and have a 3 Yrs old girl child . She is working Women With great difficulty she is building her career and ambitious too Because of doubts her husband is not willing to live together She was abused badly from his whole family and physically and mentally been affected Even after asking to come back join the family , he never showed interest to live Continous torchure at work place , phone calls and sms and doutbs on other persons too , he is also wandering to take away my sister life He left home without wanting anything and After 7 months ,with baring so much threatening and black mails now she is boldly decided to divorce. Now he is bouncing back telling he needs baby. But my sister's only hope and life is her baby. He is threatening to give baby if not he would kill her and take away the baby Now he is also bought a new concept telling let the baby be bought in Hostel so that baby will not be here with mother either father. She is greatly depressed and now what as a family we need is baby and for well living. Can anyone please reply what has to be done for this. We as a family dont expect one rupee from him but sister life should be in peace even if she is alone.Baby is her life and nothing more. Please anyone help me with answers