Do mortgagors who surrender their homes in Chapter 7 bankruptcy still have quit claim rights, after a bank foreclosure?

I recently bought a home through a sheriff's sale in Michigan. Months prior to the sheriff sale, the mortgagors, a husband and wife, both surrendered the home in Chapter 7 bankruptcy, which was completed and discharged before the foreclosure sale. Now that I have bought the mortgage, do the mortgagors still have the usual six months redemption rights, including the right to sell a quit-claim of their rights to a third party? If they were to do that, wouldn't they have to re-open their closed bankruptcy case?