This article explains the occupation of seats in the virtual classroom.
Have in mind that Moderator occupies a seat the same way the student does. If your classroom is equipped with 25 concurrent seats, the maximum number of users (teachers + students) you can have at the same time is 25.
Multiple Moderators in one session are available, but every moderator is occupying one seat in the virtual classroom.
The Session Recorder will appear as a regular user in the attendees list, but it does not occupy a seat.