You should be able to update their email in MakerManager ( Log In | Maker Manager 3 )
You log in as the primary user, and then up in the top bar under my badge is, you should see the family account that you created. You probably can edit the information there. If not then it requires support intervention - please remember that everybody including support is completely volunteer run, so some things can take a little bit longer to filter their way to the right one.
Alternatively, IT office hours usually occurred during Saturday morning tours, which is a good time to get any account help in person.