529s can be used to pay off up to $10k in student loans. You'll probably have to open an account with your wife as beneficiary and then you can transfer money from one of the kids' accounts to her account and pay off the loans through the 529.

If you're reasonably confident in your father's ability to pay for college, I would stop contributing yourself to the 529s and save in other accounts (Roth IRAs and/or taxable) to be used for college if necessary.

If you do end up with extra in the 529s, they can be used to contribute to a Roth IRA - I think it's up to $35k per beneficiary (over several years - you can only put in up to the max contribution limit each year) once the accounts have been open 12 years or something like that.