ownership

You mean bank did not have mom and dad sign as "buyers" or "borrowers," not "sellers"?  If son's name only one on promissory note, then son is only one personally liable (i.e., if deficiency left after foreclosure, bank could only sue son for it).  If all three were owners of property, then mortgage (in Nevada, is probably deed of trust) must be signed by all three, which means that if son did not keep loan current, then bank could foreclose on property but only look to son for the deficiency (i.e., mom/dad put the property at risk for nonpayment, but not other assets).  If you are saying mortgage was not signed by all owners, then it is not valid against the non-signing owners and bank cannot foreclose it.  (If you are saying you signed mortgage but not promissory note, then mortgage is valid and can be foreclosed.)  If mortgage is invalid, bank has only an unsecured debt against our son and title to your property is free and clear.  That could only happen if the bank made a mistake at the time of closing (HIGHLY unusual, so your facts may be erroneous), and bank probably got title policy insuring validity of mortgage and has claim against title company.  If son files bankruptcy and mortgage is invalid, then debt treated as personal debt and he would not "return property to bank."  Mom/dad would own the property free and clear, but might have to go through legal steps to get mortgage off record when sell property.