You need to talk to a lawyer qualified to practice contract litigation in the state where your parents lived. You also need to get your facts straight. According to your timeline the debt should be paid in full by now. You haven’t alleged otherwise. You are probably going to need 15 years of financial records, as well. Did you ever discuss this with your non-confrontational parents who apparently went after the debtor a decade and a half ago?
And, perhaps most importantly, are your parents dead or alive? If they are alive, have you had them declared incompetent and yourself appointed guardian by the court? If dead, are you the executor of the estate? All information the lawyer would likely need to know.
the debt has not been paid...as I said maybe only a year or two of payments were ever made. They are still alive but I am handling everything at this point. They know I am going to go forward with this if w are able. They never pursued because they felt “bad” making an issue. I can’t explain the sheer ridiculousness. Don’t the debtors also have to prove on their end?