We have a Toyota Sienna and love it. The boys both sit in the middle row and we keep the back row down. It fits the stroller, groceries, etc nicely. I honestly can't imagine trying to fit someone in the back seat of a car with 2 carseats. Would someone be riding back there often? If you plan on having someone in the backseat with the 2 carseats often, I'd opt for a bigger vehicle. If it's only the rare occasion you'll have someone back there, you can probably get away with a smaller car.

Also, to cut down on size of the cargo I'll be lugging around, I'm planning on getting a Sit and Stand type stroller rather than a bulky double stroller. With my two kids now, I only have a single stroller, but with a third on the way I'm planning on getting a new stroller that will hold two kids.