Is it slander if the words are sent to the police and the person gets locked in a mental hospital. When his family disagrees

My father was picked up on an anonymous tip from someone 1000 miles and 9 hrs away. That he was homicidal and suicidal. And is now at a mental hospital. Is job and reputation is on the line plus his retirement. Everyone in his imitate family, and his brothers who he is close with, plus neighbours and coworkers all stated he is no danger to us or anyone. But they still took him because of this tip. Which we know now is from his sister from north Carolina. The sister has not been to see her brother in over a year she has a bad relationship with her other two brothers. We want him out but they are listening to her instead of his family. Can we do anything