Hi Laurie,
The "grouping" filter found under Field Services Center -> My Calendar -> Filter Calendar simply filters the list of groups that you have the ability to set up when creating/modifying existing users. This feature allows you to associate users to groups and categories such as departments, however it does not associate a work order to that group.
One thing I did want to mention is that this pertains exclusively to Method Field Services Application, not Q-Xpress - it is now a separate product. Although Method Field Services allows you to enter job cost information, and assign individual jobs to different users, it does not support the ability to assign multiple users to a single work order. It really also depends on what your end goal is as assigning a single work order to multiple users introduces a wide variety of use cases (what happens if one of the users deletes or edits a work order, just as one example).
Regards,
Denis