You are obviously being put the squeeze on by your ex-in laws.  And I think that you need to take the loan documents to your lawyer to review in light of the divorce agreement.  They need to be read hand in hand and really the loan should have been addressed in the agreement a an outstanding marital debt.  Maybe it was in a round about way.  But I am sure that you are jointly liable for the debt.  If they insist on suing you on the matter then you would in turn sue your ex wife for contribution to the loan.  That will not sit well with them but you are I am sure within your legal rights to do so.  Good luck.