Custody of Child

My brother's wife left back her 2.5 years old son with us and went back with her mother. She had a fight with my brother over his illicit affairs with a girl to which even we don't approve of. My brother accepter his mistake and went back to get her wife back from her Paternal home. However, she refused to come back and later filed a complaint in the women cell against my brother, mother, myself. my wife and my sister. My brother went along with my mother to see the DSP of Women cell and told the personnel that they want to take back the wife and would also give a Mafinama in written to police to accept his mistake and for assurance that same will not happen again. However, her mother and she started telling conditions such as she will only come if my brother buys her a house on her name. My mother refused and they returned back. The brother in law of my brother is a convicted criminal and serving a term of 20 years in Jail and is temporarily out at the moment. DSP got his signature as one of the witness where as I feel a convicted criminal cannot be taken in as witness. As my mother feared that the family of the victim might harm the kid to avenge the death of their family member, she never let the wife of my brother to go alone to her native place with the kid. And the same thing she is using against my mother in a way to showcase that my mother tortured her and did not let her go see her mother. My brother seeks a divorce from her now and wanted to understand the best way to proceed. And also want to keep the custody of child as we are very sure that kid's life will be completely ruined if we allow the mother to take the custody. She comes from a family that fall below poverty line and my mother just fulfilled her long desire of helping a family by getting her daughter married to one of her son. It was a very private affair as we brought her home the very same day we went to see her for arrange marriage and she carried nothing more than two sets of suits along with her. Please advise how can we keep the custody of child and how can we break ties with her as we think that they just trying to suck the maximum money out of this bond. She transferred all the money from her child welfare account to her personal account. Regards.