That’s correct. The lender doesn’t want to do all the due diligence and paperwork necessary to take on a new debtor. Plan to refi it, or….
just informally start paying on the loan in place of your parents. If it is good rate, this may be the best course of action. Of course, all kinds of problems can crop up when family finances get mixed up like this. For example, what do other siblings say about this? Also, lender may force a sale or refi if they find out your parents are breaking one of the many covenants on the pages and pages of fine print your parents signed to get the loan.