Currently, you are only shown the groups of which you are a member are displayed for Sdui admins.
We are currently working on an "Admin Panel" where the school management will have access to all groups in the school, as schools have suggested this feature to us. It will be visible to Sdui admins, as soon as it is finished. Here, the admin will be able to view the members of all groups and will be able to remove members or add new ones.