child access

My sister she had filled maintenance case again her husband who stay sepratly from last 5 to 6 years n my sister stay with us from that time with is son Rehan who is know 5 years my sister ask her husband for divorce but her husband saying that he is ready to give divorce but he is not going to give his son Rehan.my sister husband had ask a court for access of child rehan. My sister son Rehan don't want to go with her father bcoz he had saw that how his father had treated badly with her mother and we all don't want Rehan to go. My sister husband had got second married With out my sister permission n with the second wife he had one son n that second wife already had one son means that lady husband was expire