Does an old contract have any effect on a new contract? (IN)

Just so I'm clear, since it's a little confusing as to who wants what:

Your grandparents, to save their house from forclosure, sold it to a family member, who will will call Adam. Adam wrote up a contract for them that included a repayment schedule of $212 per month.

Adam, later, decided that he was tired of this arrangement, and so sold the property to a family friend, Bob. Bob wrote a new contract with your grandparents that removed the monthly payment, instead having a clause that made the whole amount due on death.

Your grandmother passed away in 2021. Bob now wants the entire loan paid, and he's threatening to sue your grandfather over it. He's also threatened to put a lien on a different house that your grandfather owns.

Do I have all that right?

/r/legaladvice Thread