Can he file a defamation case against my family?

The boy and my sister were earlier in relationship and wanted to marry each other but later the boy's changed toxic behaviour threatened my sister and now she doent want to marry him as she knows he won't let her be happy. So my father asked him whether he is sc/st or rajput and I rajput can he give proof of their origin and being a rajput. Just because it was. Concern of marriage and everyone prefers to marry in their own caste. The question asked was never publicly asked it was just a question out of concern and it was on a phone call . My father's intention was not to defame him. Can he file a case against my father? The boy is threatening to forcefully marry her and if she will not marry her he will destroy her reputation and even her family. He just wants to take revenge . That boy is giving suicidal threats to my sister and even threatening her to get kidnapped or trying to defame my family's reputation by Makin all this case public. What to do now? That boy is lunatic and is trying everything to take revenge he tries to attempt suicide and even follows that girl. He promised us that he will destroy my family What can i do now to get rid of that boy