I haven't fully read up on this but didn't all 11 judges reason it was a justiciable (sp?) on the basis of precedent?
If so they didn't jump in at all, and the lower English and NI courts were incorrect (not the Scottish).
Also all 11 judges were unanimous, which seems unlikely if it was a...
Not ordinarily, but not necessarily not.
Proroguing prevented Parliament making the decision to sit.
Edit: And not just Parliament, but select committees etc. too.