You can't. It's none of your business and nobody's going to tell you. There's no public records on what was paid to buy the loan but likely it was pennies on the dollar since it was not performing.
Between a dollar and a gazillion dollars. In other words, nobody's going to be able to guess. A lot depends on what the house's market value is.
If it's worth a lot more than the $410,000 or so then they have you over a barrel because foreclosure is likely to pay them off completely,
If it's worth considerably less than the combined loans you can offer whatever you want but they can still hold out if they want to.
Consider taking a loan from your retirement account (if it's available) instead of a distribution. That way you don't pay taxes on it and you pay yourself back. Otherwise you can count on paying up to a third of the distribution in state and federal taxes.

