FAFSA has its definitions, IRS has its definitions, banking has definitions. They may or may not be the same. For example, the IRS and FAFSA have different definitions for ‘dependent.’ You still have to report income on the FAFSA as it appears on the tax forms (where you entered it according to the IRS definitions), but you don’t get to use the IRS definition to claim you are independent on FAFSA. FAFSA asks about cash assets, but doesn’t ask where those assets are located, so if the OP thinks the money is his, he needs to report it as his. The bank isn’t going to look at it the same way.
The joint owner of a property doesn’t have to report the entire asset. Legally, the parent may have the right to fully use the beach house owned by 4 different people, but that doesn’t mean he reports the full value on financial aid forms.
Custody (of the child, not of the account) is relevant here as the non-custodial parent’s assets are not reported on the FAFSA.