You've added owners to your groups but some do not have full access to edit everything.
With the exception of Community groups, Group owners such as Advisors, Teachers, Activity Leaders, and Dorm Supervisors need to have the corresponding employee roles added to their employment record before they have full access to edit their group pages.
To edit an employee's employment record please navigate to:
1. Core > People Finder 2. Search for and click on the user 3. Click Access 4. Click Employment 5. Click Edit > Check off the appropriate employee roles and be sure to check the Effective Immediately radio button 6. Save & Exit