Randall has the right idea.
Your parents need to get the facts, and I mean ALL the facts.
There is a wave going through our country right now that says that if you have a mortgage (which is a promise to pay a debt), you can walk away just because you want to do so. IMHO that is complete nonsense. Throughout most people's ownership of their home, prices have gone up and down...however, in the long run, they go up.
There are people who re-financed, took out cash, and now find themselves in a situation where they either can no longer afford the payments, or simply feel because the value of their home has declined they "deserve" to have their debt forgiven.
I do not know the specifics of your parent's circumstances, which is why they need the advice of an expert that can sit down, analyze their situation, and offer not only options, but consequences.