I really doubt the daughter and ex got a FSA ID with the mother’s name and email. When you get the FSA ID, they send you emails so you need to use one that you have access to - not one the ‘really’ belongs to the OP. Anyone can get a gmail address, the ex probably has all the info he’d need to get a FSA ID for the mother (name, SSN, date of birth), but do you think he’s going through all that trouble?
Also, gifts from his family are not income to him. He wouldn’t have to report those gifts unless they were still in an account, then they’d be an asset.