Sticky issue
Based of facts. I speak on this issue having served in both sides of the cockpit door, currently a pilot for the airline. One thing we all must understand. The company and the FAA have named the Captain to be the person in command of an aircraft.
A similar issue occured years ago when I was an FO where the Captain and the purser disagreed on the middle of the flight. At that occasion the Captain simply "demoted" the purser and the second most senior FA took the purser functions for the duration of the flight.
I think it was absurd and unprofessional of this UAL Captain to divert for such a reason; however, if a situation is not critical or places the safety of the flight in questionk, one should do just like the Captain asked, then later report to their superiors; but until then (and that serves for FO's too) we need to understand Captain's authority. SUch Authority is his right; not needed to be earned.
I would send both to the full initial CLR 5-day remedial training.
Best wishes to all