You can share the admin role in your Celtx Gem studio with other team members by simply granting them admin privileges.
To do so, first make sure the person you want to grant those privileges to has accepted their invitation to your Celtx Gem Studio. Then, click on Management -> Members and open their individual file. Here you can select the box to grant "admin permission."
The Co-admins will have all the same features as the Account Admin.