Scenario One: I want to be the only one that can deliver tests across a range of centres.
Site Administrators and users with the relevant Site Level Permissions are the only users that can see and use the 'Share Subject' button. If a subject is shared with multiple centres but no individual permissions are specified for Centre Administrators, the Site Administrators will be the only users that can deliver tests across a range of centres that the subject has been shared with.
Scenario Two: I want to collaborate on my question with other faculties.
Once a subject has been shared with multiple centres by a Site Administrator or user with the relevant site permissions, users with the Item Authoring permissions will be able to work on content alongside other faculties.
Scenario Three: I want to provide users with the ability to schedule tests for all subjects and centres.
When creating or editing a non Site Administrator user, you can add Site Level Permissions which enable that user to perform the specified action e.g. schedule tests, moderate, view reports etc. for all subjects and centres.