In basic groups, admins shouldn't be able to kick other admins they have added to the group, but the user interface shows the remove button.
It is just an issue in the UI, the server doesn't allow this action
In a basic group where you are a regular admin (not owner):
In the member list, move the mouse over another admin you have added to the group.
The admin must not have been added by another member or joined via link
Delete button is available
No options available