I've got a Honda MDX, which would be way too big for what you want from what you've said, but the CRV (its little "brother") from memory had really good boot space too. The Holden Adventra was pretty good for "boot" space too I think. Whatever way you go, I would absolutely be getting a stationwagon or SUV with a proper divider between the back and your kids. The thought of two babies in the backseat as well as a dog, even one in a harness, leaves me cold.

The alternative might be a "muppet bus" like the Taragos etc. Not exactly the most stylish but sooooo much space for everything and everyone.