I hardly think that it’s an unreasonable prereq to insist that, before an eviction, the one doing the evicting prove he has title to the loan secured by the house. Other than that, throw the bums out. You want to resist? That’s trespassing. There are ways of dealing with that, too.
In some states, you can't even file a foreclosure suit unless you deposit the original promissory note into the registry of the court.