We currently have 2 cars - a Toyota Camry hybrid, and a Hyundai Elantra. I have 2 kids in booster seats, they will be 6 and 8 when the new baby comes along. So it will be several years before the older one can sit in the front seat. Have any of you made it work with 3 seats in a small car? The newbie will be rear facing for at least 2 years.
Yes, well the 8 year old will need a booster for a bit longer (till 9 in my state).
So what we did is use a backless booster. Note: we only have two kids, so this was daily carpooling to school.
What worked best for our car (Toyota Matrix, though we also have a Civic) - We put the baby seat in the middle facing rear, and the boosters on the side. In our experience, the Britax Roundabout both was easiest to install AND fit best - the base itself was narrow enough that we could fit boosters on the side.
However, since my older kid (who was 6) is short, we did have to us a special extender and clip thing so that the shoulder strap did not cut across his neck.
I recommend that you look at the seats that you have and start experimenting. Borrow seats from friends also. Some of the boosters with backs are also narrow enough to fit on the side, like the Diono Radian.