So with episodes 7, 8, and 9 all having different writers and directors, how is the story coming together? Did the Lucasfilm storygroup create the basic storyline and then let the directors kind of fill in the gaps, or do they just work together with the directors/writers while they come up with each new script? Even with Rian penning the script, surely there are still plenty of places he's been told he can't go. I really have no idea how any of this works.
As far as the films go, the Lucasfilm Story Group is really just a resource made available to the filmmakers to use to facilitate continuity. The directors and writers for each film have complete creative control over their films.
TFA's story was entirely JJ, Kasdan, and to a lesser extent Arndt. Although JJ and Kasdan naturally had
ideas of where the storylines they setup in TFA would go, and shared those notes with Rian for TLJ (who also gave some notes back to JJ for tweaks he wanted to help setup his plans for TLJ), Rian has said he had as much creative freedom on TLJ as he's ever had on any of his films. The movie he made was 100% his through and through, and he wasn't beholden to some rigid grand scheme JJ and co. concocted. Meanwhile, while Rian did a story treatment for Ep. IX and gave a lot of notes to Trevorrow, and I imagine JJ and Kasdan passed off a few minor notes and ideas as well, the treatment got torn up when Fisher died and Trevorrow started over from scratch and will, as with JJ and Rian before him, be making the movie he wants to make.
So basically:
- each director/writer team has full control over their movie
- the teams give each other notes to help set up their own movies and explain what they had in mind when they set up their various plot lines
- none of those notes actually have to be "obeyed"
- the Story Group is available to give directors/writers an easy way to maintain consistency without doing the research for themselves, and help with background elements (like, "this existing ship would be a good thing to use here, since it was built by ___ and used for ___"), but doesn't actually take the reins
- each director/writer team has full control over their movie