To save my girl

6-7 years ago my aunt married her daughter to one guy. Here the guy was too bad and he tortured her in all ways including sexual torture also. So after 3-4 years she come back to her mother's house and staying with her mother only. Means she stayed without her husband for 2 years and 6 months. Also they had a 5 years child who is mentally disordered. Now she wants to continue her studying and want to settled good and want to take divorce. But now her husband came back with son to my aunt's house and saying that ....I went to Bangalore regarding my son's health condition and the doctor said our son will recover with in 6 months but myself and my wife need to stay at Bangalore for 6 months and to take care for their child. Like this he said. But it is all drama and we are sure that he has some plan to kill or to do anything to our girl. He is such a bad person. Our relatives also forcing her to go because of the child. But we are not sure and we are not safe about the girl. Please advise the best suggestion to say our girl and to escape from her husband.