You're absolutely right that they aren't in a parallel institution. As I understand it, the SF perspective is that there is no legitimate government representing the people of West Tyrone (other than Stormont, which is complicated). I think it sounds like we're saying the same thing but there's a subtle interpretation difference. When Idi Amin declared himself to be the King of Scotland the Scots didn't send representatives to Uganda to form a government. The SF position since their Árd Fheis before the 1919 elect has been to treat Westminster like Idi Amin. To simply engage in a conversation about Idi Amin's claim to the throne of Scotland would be to give him too much credibility.
So the core issue, from the Republican perspective, is that the people of West Tyrone are denied representation at the national level in Ireland by a foreign government. Once that representation is achieved the SF representatives will participate in it. (again, not trying to address the merits; just clarify the logic)
So the core issue, from the Republican perspective, is that the people of West Tyrone are denied representation at the national level in Ireland by a foreign government. Once that representation is achieved the SF representatives will participate in it. (again, not trying to address the merits; just clarify the logic)