If the money has already been issued there isn't any recourse I am aware of. It unfortunately won't matter if your husband has contributed to his son's expenses overall, even if it turned out to be fairly equal all things considered, because all the IRS is considering is back child support balances.
So if your husband owed back child support, that's one of the only debts the stimulus can get held up from, and they have stated that more often than not its supposed to be collected and redirected to the guardian of the child where the back child support is owed.
I have a father in law that hasn't received his stimulus yet neither..how long does it take for them to send the back child support to the guardian of the child