I would definitely not use an autorun event - that will cause your game to hang. I also wouldn't use a parallel process event - you'd have something running 60 times a second when you MIGHT only want it to run every half hour.
I would set up a common event with NO trigger, that turns a switch off. Then have your nested conditional branches to test if all of those actors are in the party, and if they're all there, turn the switch on (this is a switch, not a self switch).
Then remove the first page from your event, and condition the second page by that switch you've set in your common event.
Finally, on any event that adds or removes a party member, do a Call Common Event command to update the switch depending on who's there and who isn't.