You wouldn't really be paying twice. If you personally received the 1099-R, then you would be responsible for paying the taxes. He would get a refund when he files his return for the overpayment as long as he doesn't include the same income on his return.
It comes down to only one of you should get a 1099-R for that disbursement. Whoever gets the 1099-R is the one that pays the taxes. The other person is the one that would not pay or would get a refund if they already paid.
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