With the news of twins, I have been working on buying a car. I think that I did a reasonably good job of handling the process, so I'm going to describe what I did here. I hope it can be useful to others.
The first step was to decide if we needed a car at all. Thanks to folks who commented here, helpimg me figure that one out.
Then we looked at how little car we might be able to get away with. For example, could we buy a larger sedan? It was easy to do some measurements and see that we couldn't fit all 3 kids, in car seats / boosters, across the back row. However, what if we put the big kid in the front seat, and the twins in the back? This is fine as long as there is only one adult. I figured that most trips only have a portion of the family, so using 2 cars for whole-family trips would be tolerable. However, the law in WA state will change next summer to say that kids can't sit in the front seat. And it's safer in the back, too.
It didn't take long to eliminate station wagons, either, as they wouldn't fit the 3 kids across.
An SUV that could fit us all (think 3rd row) would probably have terrible fuel efficiency, and conserving fuel is important to me. I also want to spend less, and put less weight on the road.
So, that means a minivan.