Don't know if anyone has mentioned this idea, but I just got of those prams where bubs sit one if front of the other. it's nuch better IMO than the side by sides, as it doesn't create space issues when in shopping centres or trying to get down shop isles.

I picked up one called a 'Lite Limo' for $26 on ebay, it was in great nick, and folds up to the size of my regular single four wheeler. Don't know what you think of that, but I'm loving it!!!
if it fold up the same size shouldnt be a problem