We recently introduced the concept of "tagging" not only to the Monitors but also to the Team Members aspect of the application as well. This will enable you to have overlapping groups of users, which was not possible previously. 

To be able to set this up, you'll first need to add a few Shared Users to the Team Members section of the platform. Once you've done that, all you'll need to do is to select the Team Members you want to Tag and then select the "Add Tag to X Users" in the dropdown: