Current Setup

We have a setup with several teams in the following way:

Project A (Project Area)
 |- Team 1
 |- Team 2
     |- Team 2A
     |- Team 2B
     |- Team 2C
 |- Team 3

The categories are organized as follows:

Category                   Associated Project/Team Area
--------------------------------------------------------
Unsigned <Root Category>   Team 2
 |- Category 1             Team 2
     |- Category 1A        Team 2A
     |- Category 1B        Team 2B
     |- Category 1C        Team 2C 

Each category is assigned to one of the sub-teams of team 2. Team members are assigned to either one of the sub-teams Team 2* or Team 1 or Team 3. There is no member assigned to Team 2.

Goal

I want all team members that are assigned to Team 2* to see the whole plan. Team members assigned only to Team 1 or Team 3 may not be able to see the plans.

What I did so far

The owner of all plans that we have is Team 2. When using "Restrict Work Item Access" on Category 1 (and therefore on all subcategories) then I can restrict the visibility of the work items to those members that belong to the team where the work item's "Found In"-field is set to the appropriate category.

For example:
    Story: "As a ... I want to ... in order to ..."
     |- Category: "Category 1A"
     |- Owner: Member of Team 2A

When a member of Team 2A now shows the plan he will see that story. However, a member of Team 2B will not see that story in the plan.

I know that the reason for this behaviour is the fact that the members are not part of Team 2. However, I guess I'll loose some functionality in case I add all the members to the sub-teams to Team 2 as well.

Question

So how can I achieve my goal. Are there any best practices to organize team hierarchies that I'm not aware of? Or is it common to have members being part of two or more teams?