Forced religious conversion

This is for my sister. She is married to a Muslim guy under special marriage act. She got married in april 2010. They are living together in seperate city. None of them r in contact with their families and no question of conversion. Now she delivered a baby and both sides family are getting in touch with their own daughter/son. Its only to me she has told that now the guy is forcing her to get converted. She din't want to go for conversion and have mutually decied between each other prior to marriage. Now the guy is forcing her and threatening her to hand over the baby to him and walk off. Still my family and relatives are not aware of the issue. How can this be sorted out. What legal help can we seek.