Your local courthouse is where you would go to file an eviction lawsuit. If you are not well versed in court procedure, I highly recommend that you contact an attorney prior to filing your lawsuit.
I would call the cops. If they are not on the lease, they should not be living there.
Answer
It is likely that the police could not eject the person unless they were a trespasser who entered...
You would likely need to sue in a court of equity for a judicial order revoking the life estate. You would need to present compelling evidence to the court to support your cause of action. You should...