When I posted about how we were thinking of getting a car, and specifically that we were thinking of having three kids in car seats across the back of a hatchback, several people told me they wouldn't fit. This is a common enough view that there's an econ paper about it: Car Seats as Contraception (which I disagreed with). When we decided to share a 2013 Honda Fit I was pretty confident it would work since I knew how wide the seats were, how wide the space was, and I had done something similar with a different collection of car seats. But I hadn't actually tried our particular seats in this particular car.
With the baby getting closer, about a month out, I put the seats in for practice. I tried two different ways:
The version with the baby in the middle fits the easiest, with enough room to use the wide booster. On the other hand, that requires getting the baby plus carrier farther in, which could be awkward? The version with the baby on the side does work, but you do need to use quite a narrow booster seat in the middle.
These three car seats are ones we chose for being narrow, but there are still many options at this size. This is a 17" infant seat, 17" convertible, and either a 17" booster (baby in the middle) or 13" booster (booster in the middle).