If you don’t like the deal, go to a bank and borrow the same amount of the debt remaining and pay it off. If that doesn’t make sense because it is a higher interest rate or some other drawback, then deal with whatever the terms are. More than likely the terms are still better borrowing from the relative, term life insurance is cheap and banks don’t die so assigning a beneficiary if something were to happen to him is logical.
Remember the lesson learned, never borrow money from relatives or friends.