Yes, when you go to your family and friends link, click on the individual person and click the box that says "this person frequently travels with me". That will make them your "family".
When doing FP+ for everyone, make sure that each guest that has a MDX account is friends with everyone else that has an MDX account. Then, make sure that each person that is managed is also "friended". You can do this by the "invite through mutual friends" link on the Friends and Family page. Once each person has access to everyone else's accounts then you will be able to make FP+ for the whole group!
Hope that helps! Let me know if I can be of any other assistance!