Harassment and Dowry

Hi, My sister got married in Feb 16. He stays in gurgaon and my sister in native place with his parents.Later on she came to know her husband is having physical relationship with his bhabhi. After 2 months of marriage She caught them both together in the toilet, she asked her husband about the scene, he shouted her and said he had went for toilet as soon as he entered in the toilet he saw her bhabhi he came out. Same day her husband went to gurgaon and bhabhi went to Lucknow with her husband. My sister discussed all this story to me, i spoke to her husband elder brother on the incident and also told him your brother is torturing my sister that he dont want to stay with her. his brother said he knows everything my sister is phscy, she doubts on everyone, you take her with you and fix her marriage with someone who is verymuch obedient to him. After lots of discussion he said nothing will happen he will assure they will stay together. he will go to native place and they will discuss and everything will be solve, no need of you to get involve in this matter. Later in june they met my sister and started doing harassment. My sister said his husband and his brother ate playing game. She came to know from her mothers-in-law that they also know my sister's husband and bhabhi have physical relationship but we thought after marriage everything will be fine but it has got worst. I have the recording of the communication between my sister and her mother in law. After few days when my sister called her husband and asked her when he is taking her to gurgaon he said i dont want to stay with you, suddenly her bhabhi took the phone and said if you wants yo stay with him in gurgaon than bring Rs. 5 lakhs so that he can purchase house over there, her husband and elder brother said what bhabhi is doing do so or else you stay in native place or go to your home. I will never bring you to gurgaon and i want divorce. He is evertime harassing my sister and says go from my home or i will kill you. 2 days before my wife spoke to my sister husband he totally blamed my sister and said take her to your place. I want divorce. My wife tried to convince him. She said him forget everything and give one more chance to marriage. He is not listening and saying he don't wants to stay with her. My sister says she don't want to divorce him because she know society will blame her. She is also afraid of him that he can do anything with her. Please suggest what should we do. What legal action should be taken. Pankaj