I have one 20 month and two seven month olds. I found there's only one twin pram with a toddler seat and it's about $800 for the set. EEK!
I bought a side by side jogger but sold it because theyre far too bulky and heavy, and i couldn't use a skateboard with it anyway. I now have a Valco twin runabout side by side stroller and I love it, $250, weighs 6kgs and folds to nothing, and suitable for newborn to 17kg each. At the moment the oldest stands on the front when i'm by myself, and goes in a single stroller when i'm not. I'm buying a skateboard for the oldest very soon. I used to use a sling to carry one baby but i'm pregnant and they're too heavy now!
Before you buy anything make sure it's as light as possible, and fits in the car along with the shopping etc, and will also fit through a standard doorway, my first didn't do this and it was the most frustrating thing! If your back and front pram is good though stick with it, get a carrier for while the baby's little and a skateboard for when it gets too heavy for you, portability is the key with lots of littlies! Good luck with the kids and pregnancy.
Kelly, 22, 1 @ 25/1/04, 2 @9/3/05, [email protected]/4/06