i typically train two or three clients at once. Currently only one of them can book the appointment and then must notify the others. Consequently, only one is charged a "session" for the appointment. This appointment also only appears on the booking client's calendar, not on the others, making them less likely to use the app at all.

If I book these appointments manually, they show up on ALL client's dashboards if I've elected to have classes visible (which I have for the class I teach), and it looks as if anyone can book one of these partner appointments.

If two clients train together, they should be able to BOTH book the same partner appointment, and this should not be visible to other clients. It isn't a class, it's a training appointment, just not 1-on-1.