Daughter in law complaining son is not talking

My daughter in law has anger management issue, had several heated arguments & she man handled my son, several times , she manhandled & threatened to kill my wife . My son is out of country for education .He may stay there for more than 2 years. He is very much disturbed, mentally & physically. We both are senior citizens staying in our home. Due to domestic violence & threating, her father was asked to take her back to his home. Daughter in law is currently staying with her father in another city. Now, daughter in law is insisting, my son should talk to her, should answer her mobile massages. When we communicated, son does not want to talk to her. Daughter in law, as well her father is calling us & are forcing us, insisting our son to respond. We already informed them, son does not want to communicate/talk. As our son is out of India, we are not looking for police & court proceedings. We feel that he should not be disturbed & should concentrate on his studies as well we should live in peace. Please advice what we should do? Thanks in advance.