Please imagine the following situation: The database “Team” is filled with soccer players and their emails and fields - works fine. - no registration necessary
The PrivateMemberData is filled with registered footballers - with password, also OK !
Everything good - all works fine until the following is coming out:
A Team Database Member (=footballer) wants to change his address or his availability, how does he do that? 
I have tried the following:
Put a registration in front of the database before team?? how do I connect the ID or the two databeses?
Which is the right approach, safe and secure?
Thanks to all the professionals out there