Bigamy

Sir my sister got married in mr x and they lived happy life till they gave birth to female child then the trouble started mr x left my sister in our house when we tried to convince him he assaulted our family members so we kept calm and did not go their house a gap of 1 year took place and when we went to mr x place to talk with them he did not open the door we returned and next day we got a call from local police a case has been registered against us so we got some doubt and in our inquiry we came to know that he had married another girl within 6 months of leaving my sister in my house latter mr x gave birth to male child with second wife and HERE TILL NOW HE DID NOT DIVORCE my sister and when we lodged a case in police station he says he did not marry her but he is in LIVE IN RELATION SHIP with her both mr x his second wife mr x father mother brother lives in same house and i got the birth case sheet of mr x second wife baby in which he signed relationship as his wife MY QUESTIONS 1) IS this proof of hospital case sheet is enough for his second marriage 2) as all four are residing in same residence will all be eligible for punishement 3) as i cannot get second marriage certificates or photos can i fight this case or should i leave it 4)my sister till now did not apply for maintenance also now we want to ask judge to return our dowry money will we order him to return our money 5)how can i prove that he had second marriage so that he gets seven years punishement