You are really beyond the scope of what can be answered here.
You need to sit down with a lawyer for a paid consultation to figure this out.
The short answer is the principle that a thief cannot convey title, but you have complications that would need to be evaluated.
I believe they could be innocent victims, just as normal tenants are. I wouldn't take a chance on an early eviction and would follow federal law. They do have an obligation to pay rent while they are there to the new owner. You can review the law to see if any exceptions apply. http://www.occ.gov/publications/publications-by-type/comptrollers-handbook/ptfa.pdf