Son and Daughter custody

My friend stay in Bangalore along with her daughter. She studies here. While coming from his hometown to Bangalore wife denied to come a day before boarding the flight and she kept the son and send the daughter for her studies. Now when he is asking her to come back she is not telling time frame when to come as she wants to fight for her fathers property against her brother and take care of her disabled sister. She has 3 sisters. When he said if you want to stay then stay atleast give me son as daughter is really missing him and getting depressed. Now she has blocked his phone number and his daughter number. Its been more than 20 days that there is no information about son and wife. All 4 sister is staying in their parental property and fight the case to get there portion of money vs brother's. My friend said there is no need of property just send son and stay for how long you want as daughter is getting panic and not able to concentrate on studies. His Son is 3yr old she didn't even allow him to get the school admission done. In this case what can be done. Son 3yr old Daughter 11yr