First of all, if a seller defaults on his or her loan and misses 3 payments, the lender usually starts foreclosure procedures. It seems as though the sellers in this case were in default and you may not have been aware of it, so one of the things the seller can do is try to stop the litigation. In this case you should consult a real estate attorney to advise you and guide you in the right direction.
I recently closed on a property that was in a very similar situation. Depends on how far the litigation process is, the attorney should be able to help you.
Good luck and best wishes.