Need a suggestion regarding my sister divorce problem

Hi, my sister got married 7 years back. She has two kids one age is 6 years and other age is 4 years running. From past 7 years she has a problem with her mother in law and husband. When my sister is newly married her mother in law use to trouble my sister for dowry. And her husband by listening to his mother words he is use to beat my sister. This is continuously happening from past 7 years. Three months back we have given complaint in women police station and her husband gone through counseling, because of that reason he started torchered my sister more with his words and by beating her. One day because of all his torcher my sister health got spoiled and she is admitted in hospital. Later he left my sister in my home and went. Due to health condition we thought of keeping her for few days in my home. From that day to till now he is not allowing my sister to talk with her kids. If my sister call to him he is disconnecting call and not allowing to talk with kids. From past 2 months my sister is in my home and kids are with her husband, is this will be a problem to my sister?. Now he is asking for divorce. Please suggest us how to get out of this problem. My sister is not ready to give divorce and she want her kids.