Display content by specific groups of users
The simple solution would be to add Term Reference field to the user's profile fields. Then for each user assigned them a taxonomy (in this case the taxonomy term name would be the group name).

Use Field Permissions module to control who can edit and change the user's tax reference field.

Use Views and filter by taxonomy term to display the "group's" content. You  will need to make a View of Users then under Advanced (far right) add a Relationship of Content authored.