Child Custody

My brother and her wife has a dispute since last 1 month. The dispute was regarding my brother was jobless since last 1 year. But now he has joined a new company. Now she left his house with his children and went to her mother house. The small boy is of 3.6 months and my brother was not ready to give him. She put a fraud complaint that he is making harassment and not giving a child to her. As per police the boy is 3.6 years old so please give it to her mother. The small boy is not emotionally connected to her mother as full day he stay with my mother. As it has already crossed a 20 days she is not ready to come back home, neither she allowing my brother and his relative to meet that boy. Her mother is making a fraud statement that she will file a complaint as you people are coming and making fighting with us. The boy is so attach to us as whenever we are going he is crying to come back home. As we have already made his admission in Jr. Kg. his school is also missing. As she is not picking our phone to allow us to talk with child. Please advice in this case.