They have deprived tax payers of money they aren’t legally entitled to. The defence of legitimacy has no bearing as part of the requirement for that defence would be having to swear a oath to the king. Winning the vote is one part of being elected, failing to complete the second part removes that legitimacy. Parliamentary protections and immunity would not apply as they legally cannot hold office until they swear that oath.
This isn’t even a monarchist or non-monarchist thing, it is a matter of our constitution is very clear as to the requirements to sit in office and they refuse to follow those requirements. The province cannot unilaterally amend the constitution. If they get everyone on board to amend and remove that portion thats one thing, but this unilateral nonsense needs to stop.