I finally tried bike + child seat + trailer bike combination this week and it worked! The only problem is a bolt that hangs down from the child seat and scrapes the trailer bike, but there is a plastic sleeve protecting the frame and i'm going to file the offending bolt down this weekend.
The one thing about having 2 kids behind you is that cars do seem to give you a lot more room, but I only have to use the road for a tiny stretch as there is a cycle path for most of the way to the school, although it is covered in glass in parts. I've been tempted to bring a dustpan and brush with me.
You get quite a lot of people smiling at you and kids saying cool, but I dont see many of them getting out of their cars and doing the same. Who knows - one day it might be their only option.