LB
CASR 91.220 (b) and (c) are the critical bits of regulation which give the right of the PIC in this instance.
Was the instruction lawful? There is an implied delegation to the CC under 91.220(1) which stipulates the 'operator' being the airline as I read the regulation. Now a curly one, - and it is not mentioned - is there an automatic delegation to any crew member for duties within their responsibility? Or is it up to the PIC only to make the request for assistance?
Also, is a CC member who works for a Labour Hire company, an employee of the Airline. No they are not (applying the precedent in the mining industry and the recent High Court deliberations re contractor v employee arrangements that has the ATO in conniptions) but the operator does owe them a duty of care as if they were an employee.
But the critical issue turns on whether the command to sit in the assigned seat was a requirement - it clearly was not necessary for the 'safe' operation of the flight - which then must be translated if the command was necessary.
I know what my judgement would be if it came up on my list for mention.