You should only add an email address to the profile of the person you're sending the request to. Adding someone else's email address, for example, adding your son to his cousin's profile will make them a manager of that profile and that becomes an active family member profile when they accept the invitation. If your son wishes to join, he can either make an account or you can add his email to a profile you created for him. Do not add his email to other family member accounts unless he is already an active member. And then only add it to the privacy tab to add him to the trusted list, not in the edit tab.