I can probably start us when it happens. I can take the role of Sansa if needed. I assume some roles will be shared, depending on what's going on since waiting for some words to be exchanged in the next post seems a bit annoying so backtracking or sharing would be needed. But generally with most "adv" posts this isn't too big of an issue.

If we don't bring Cat down from the Vale to K.L, that's fine by me, Ned still needs to keep his head on one way or another I think.

I would say tv ages for the sake of ease. I know they're younger in the books but if we wanted to, we could just state their ages now so we're both on the same page. 

If you're fine with me play Petyr and Sansa, that's fine with me. I figure I'll have Petyr make his own plans to get Sansa out for Cat, as well as to throw things off in the city itself. While he'd want to stay and keep tabs on people, he has his own spies to do that for him. So him taking Sansa out and following soon after, might not raise as many flags. Or he could stay and have Sansa being transported by someone else, Bron or some nameless idiot.

If we had Arya with Syrio at the apprehension of Ned, (assume Sansa is gone at that point and could be easily claimed a traitor for "running away" from her betrothed) it would make Joffrey act a little less like a shit. I assume Arya would be contained to her quarters until the mess is resolved? Or Arya, sensing her danger could find a way to sneak out, which we could have Joffrey go after her or we wait? If Arya stays put and Joffrey decides to show mercy, we could have Blackwater happen, or we could push it up a little bit. I don't know. Either way, Sansa vanishing and Ned trying to talk to Joffrey about him being unfit for the throne, Joffrey has a lot on his plate. Either Arya would try to get away or she could try and play along for the sake of staying alive and have them leave the city after Blackwater when the city is rioting. Or during, it depends when we want them to go as it will change the dynamic from a political one to just one of survival and figuring out who to trust.