I have a house that I allow my 76 year old Dad to live in for free. He is allowing a worthless couple to live there and I want them out. What can I do?

You give them a written eviction notice... you are the property owner I assume and not your father.

Its 30 days to vacate in most of the country... but 14 days in Florida and 60 days in California. At that point you file with the court to have it enforced if they have not left. When you win the sheriff will put them and their possessions at the curb and you change the locks. And tell your dad if he does it again he goes next.