I agree that your Ex might be the best one to claim the credit, and if he gives you the money he gets back, it could be the best way to go. He should not give money to your son, but to you, as any money given to the student by a NCP (or anyone other than custodial parent ) is reportable on FAFSa as untaxed income.
It can take planning to figure out the best way to pay the very least in net to a college when tax credits,merit money, financial aid are all involved. With a NCP in the picture it can get even more complicated. It’s very helpful that you and the ex can work together.
Is your ex going to be within the income limits with modified AGI to be able to take AOTC, get more financial advantage than you will?