Good question. Since he does not receive the refund, I think you would be safe. But I would check with the IRS to be on the safe side. The refund is not in his name and is not for his income producing activity.
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If your father-in-law meets the qualifications to be your dependent, then you should claim him. I know of no law that would make you liable for your father-in-law's debts if you claimed him as a dependent nor one that would authorize Oklahoma to take your refund for doing so.
I do not believe that the IRS record of your tax account for each tax year would even show collection attempts by Oklahoma against your father-in-law because those attempts will be on refunds due him under his social security number and your account is maintained under your social security number.
You may want to review this your tax preparer as well as the requirements for claiming him as your dependent. Also, you may want to check with the IRS as recommend by Attorney Cohen. They shouldn't take your refund, but I am sure all of us have seen things happen that we believe should have happened.
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