Yes, with the accounts in his name, he's legally liable for the balances.

Sure, you can attempt to negotiate a discounted lump sum settlement with the creditors.

But why bother.

Why not just ignore them and use the money for your father's care.

Eventually there won't be anything left for the creditors to get.

Just make sure you get his money out of his name and stash it someplace safe.

Above is not "legal" advice.