First off congratulations!!! I hope you have a healthy pregnancy and healthy babies, and are able to maintain your sanity in the process
Thanks for stopping in. As other posters have said, we do recommend rear facing as long as possible- this helps explain why-
[ame="http://www.youtube.com/watch?v=sssIsceKd6U&feature=player_embedded"]YouTube - Rear facing vs forward facing position in the car[/ame]
You have gotten some good suggestions on seats and vehicles. I have an 05 toyota sequoia. It seats 8 comfortably, with a real cargo area in the back, not just that smidgen of room that some cars call "storage"
I have had a regent and boulevard side by side in the middle row with room for another full sized adult, and have had five car seats in it at once- that took some puzzling but wasn't as bad as I thought it would be. The middle row of mine is a 60/40 split, and the rear row is a 50/50 split. All seats can fold forward, middle row can completely tumble forward or be removed, and rear row folds forward, can scoot forward to touching middle row (allowing even more cargo room) or be removed completely. I can't say enough wonderful things about this vehicle. It's reliable, and VERY car seat friendly. (not sure about newer models, but I

mine).
Good luck in your decision making, and thanks for stopping in- we like to see parents taking the time to make sure their kids are safe before an accident happens.