You definitely don't want staff using their personal Facebook accounts. The Quest 2's browser auto logs in to Facebook without needing a password (since you are already logged in to Facebook to use the headset) and you can't stop it (as far as I've tested), so the students would have full access to the staff member's Facebook page and Messenger.
The best solution is to get the Business edition of the Quest 2. It has no Facebook account requirement and is intended for multiple units to be managed together. Sadly it costs $799 each, double the price of the normal Quest 2, and has a yearly subscription fee too.