File a claim for surplus funds on real state property

Are your parents still alive?  If so, they need to contact the lender for any overage received on the sale.  If they are deceased, and the amount is less than $150,000, you should be able to contact the lender and supply the lender with an affidavit.  Most lenders will have the form.  If the amount is in excess of $150,000, or if there is other property in your parents' names that, in total, is over $150,000, you'll need to open a probate administration.  If the lender sued your parents and had the court do the foreclosure (that is actually rare), then you (or your parents) would need to apply to the court to obtain the funds.