I'm pregnant with #3, due in mid-September. I drive a 2008 Honda Odyssey. The plan is to put the baby's seat in the driver's side captain chair. I'm assuming we'll start with an infant seat and move up to a convertible at about a year old. However, I have NEVER carried around a bucket seat, and can't fathom I'll start now, so I'm willing to consider an awesome convertible that would fit a newborn well (DD1 was 5lbs 14oz and 19 in, DD2 was 8lbs 0.5oz and 21in) and would work well for long term rear facing. We spend lots of time in the car. I want a seat that is very cushy/comfy for baby and very easy to buckle, unbuckle, adjust straps, and install (though we don't move seats often at all). This is our one big baby need, and like I said, we spend lots of time in the car, so cost is not a major concern. What seats should I be looking at for baby? Anything new coming out this summer I should be looking out for?
DD1, 5.5 yrs, rides in a Nautilus. She has plenty of room left, and I'm planning to keep her in the seat, which we're perfectly happy with. However, she can not undo her bottom buckle (she can buckle herself and undo the chest clip, so maybe she'll master the bottom by the time baby arrives), so I may consider a change to full back booster if I feel like she's ready and could do that buckle solo. I plan to put her in the third row, and being able to buckle and unbuckle herself would be a HUGE plus. I'm only 4ft 10in, so I doubt I could reach the buckle without climbing into the van around the 2 RF seats in captain chairs to unbuckle her. DD2, 2.5 yrs, rides in a Boulevard 70. She's tiny, and I plan to keep her RF in this seat until close to 5 yrs (as I did with DD1 who's been FF for under a year). She'll ride in the passenger side captain seat.
FWIW, DH drives a 2005 Honda Civic. We currently have a RF Boulevard for DD2 (this will likely expire in the next year or so... I'll have to check it) and a FF Complete Air for DD1 in the back seat. The idea of 3 across sounds overwhelming here. I'm assuming that whoever has the baby will have the van, but DH does have the older girls often mostly on the weekends, and I drive the van almost exclusively, so we may want to consider options for this car too. I may be willing to consider FF DD2 in this car, though our preference would be RF. Any suggestions?
Convertible wise, I'd look at a true fit or a Graco Myride. Lots of infant paddy, very comfy. Do you have a split seat in the back? With an older child, you could fold down part of the back seat and she could get in via the trunk if it's easier than crawling under a rfing seat. Also would allow you to reach her easier. Your dd1 would be perfectly safe in a booster, if it's easier for you, as long as she can sit properly in it. Most kids can by age 6.
As for the other car, I would just figure whoever has 3 kids has the van. And once baby is big enough for the blvd it would be easy to adjust as needed between the younger two (and you could put your middle dd ffing in that car if it's just her and baby for the trip). And when it expires you could look at another adjust the harness from the front seat like another blvd or a complete air. But I realy wouldn't worry too much about that car right now, it's probably rare your husband will take the baby early on anyways. If you find you really need a 3 across option in that car at some point, you might want to consider a bubblebum booster for your oldest or a RSTV for your oldest or middle child.
Also look at the Maxi Cosi Pria. If your new baby is tiny like DD1, this would be a great choice. It has a super tall shell for extended RF, but because of the "tiny fit" insert, it doesn't take up much front to back room.
With 3 until the 3rd got a lot older, who ever had the 3 had the big car and if DH just had the 2 girls then he took his car. We only kept seats for the 2 girls in his car, if DS1 was going along then they would take my car. You could tumble a chair and put 2 in the 3rd row like another poster suggested or just take out that seat. Start working on getting your DD to buckle herself if you want to use the 2 captains chairs. i always loves it when they could finally buckle themselves in!