We used stroller #1 last week for a 6 year old and a 3 year old. They both fit fine and they even managed to fall asleep in the stroller when they needed to. Here are a couple of things I discovered:
Some of the gates at the MK aren't wide enough to roll this stroller through easily. Look for the wider gates, or have the kids walk through so you can tip or fold the stroller to get it through.
The stroller doesn't have an official rain cover, but a dollar store poncho and some clothespins do the trick nicely to cover it if necessary. We left a poncho in the pocket of the #1 stroller, but you might want to bring some kind of clips (we actually used little caribiners that I keep in my diaper bag).
I have pictures of the kids in the stroller. Let me get them organized and I'll post.