Assuming each family only has one primary account holder who is the person who logs into MDE, and everyone else in that family is a "managed by" profile under that account....
Log onto MDE and add the other primary account holder, and fill in their email in the "invite to plan and share" section. Then wait for them to accept your friend request. (Do NOT try to add the other members of their family yet)
After they've accepted, then you can use the "add friend from mutual friend" feature to add all of the other people on their account. The primary account holder will then have to accept each request.
Lastly, they can request the profiles that are managed by you so that they see your family.
The important part is to not try to add any "managed by" profiles until you're friends with the primary, and then add them through mutual friends. Otherwise you can end up with multiple versions of them.
-Rob