Remarriage of Widow with a widower

Dear Sir,
Let me brief the family background of girl and boy first. This girl is a widow with 8 months old son. Her husband died of cancer when her son was less than 3 months old.
There is a boy (Govt Servant) whose wife died one year back. He is having 4 years old daughter and one years son. Both the family belongs to upper middle class family. both family want them to remarry. The problem is.....
Girl's in-laws does not want to part with their grand son who is only 8 months old and is only offspring to their family. May be thinking of their family name and about their last rituals. Girl also does not want to leave her son for remarriage. Boy's (Widower) family is ready to marry the girl with or without her son. Any decision in this matter should have consent with both the families hence the matter is not moving forward due to girl's son issue. I being one of the close relatives of that girl, want that the girl should remarry with the boy keeping her son with her. Now what legal recourse is left in the situation when girl's In-Laws are not ready even to take the son with that girl outside (may be in the market or her parents house).
Kindly reply