Most lenders will have a clause in the agreement with the seller that this be an arm's length transaction. Part of the that is an agreement that the former owner is completely out of the situation once completed. I wouldn't rent it to a former owner if I were you. You both could be charged with fraud. Doesn't matter if you didn't know them at first.
My experience and opinion, of course.
Remember the old Clint Eastwood chararcter of Dirty Harry.
"Do you feel lucky?"