J.S.
I have a Phil & Ted's tandem stroller. I didn't want a side-by-side as I can't imagine navigating stores/the mall with that. The Phil & Ted's seems more "sporty" in that I use the stroller 90% of the time for walking in the neighborhood so it was more "physical." My toddler (2 1/2) sits in the front, and the baby (10 mos) sits in the back in an attachment that I hook on.
http://philandteds.com/en/productsus/pushus
I think it would fold down well to fit in your trunk.
The drawbacks is that it doesn't have good storage, so if I go to the mall I carry my purse, bags, etc., though I can fit the diaper bag in the bottom. The unfolding is also a little tricky, and the tires are real tires, so I've had one "pop" due to glass so I had to take it to a bike store to be fixed.
I bought mine on eBay (new), and probably paid $100 less than if I had bought it in a store.
I have the "Sport" model which I'm not sure they're making anymore. I should've bought the next version up (Deluxe?) as I don't like the brake on mine. They're also not cheap ($400-$500?).