Roles and permissions

Firstly, let's be careful about the term 'Administrator' this really only applies site-wide.

If you want some variation on the 'Manager' role (or just Course Creator) you could look at separating the organisations using Course Categories. Roughly speaking, you can then assign your managers to the relevant Course Categories.

What you can't do is to restrict role assignments to groups of users (not in any useful way that I can think of anyway)

Failing that there are some commercial forks of Moodle out there that do just this. They give a completely unique, discrete view for users from different organisations/companies on the same Moodle.