Add multiple @groups to valid users
Solution 1:
Just add comma ',' if you want multiple valid users. See line that I used below.
valid users = @group1, @group2
Solution 2:
I wound up adding the users from the most restricted group Directors to the Staff and Interns group as well as their original group. Then I added the users from the Staff group to the Interns group as well as their original group.
The line I used was a simple
valid users = @group_name