GGV, as usual you put it more succinctly than I or others could ever put it.
I cannot answer your question. However it could happen to me or many others here tomorrow and we would have to act without the legal opinion we all desire.
We are parked off stand. You want to get off. What am I legally obliged to do to comply with your legal rights?
Most of us would plead, persuade said pax to stay aboard....reassure any doubts etc but after that if the pax was determined to deplane we would have the original problem.
Irish courts have tended to back up Irish crews quite well with disruptive pax in the recent past but this is different.
*You are not in flight by any definition and the doors holding the pax were closed by your crew.
*You can argue semantically about no steps, but that does not reasonably give you the right to force the pax to remain on board for a flight which they dont want to undertake and which hasn't begun yet.
It is a massive inconvenience to all involved not least the other pax to have the perpetrators disembarked but in the absence of clear legislation protecting me I will be letting them off. The only thing I might consider is a chat with the local constabulary but that really would be a last ditch effort to persuade the pax to remain on board.