Is there any solution here that I'm not seeing? I think that even if the two older ones are in backless boosters, there isn't any way to fit a harness seat for the 4 year old back there too. But I'm used to the bulky Britex seats, and maybe there is something smaller? Or, what larger cars have people moved to? We also have a problem of not being able to fit my mom in the car with us.
I'd appreciate any advice!
Yes, there is definitely a way to do this :-)
Can you be specific about which boosters and convertibles you own, and their dates of manufacture? (Britax is the brand name, not the name of the seat, and there are dozens of possibilities.)
Also, is your two year old rear facing? And which year is your Oddy?
One more thing, can we get the heights and weights of your older kids, and the heights of the younger ones?
ETA: Congratulations on your pregnancy!
Also is your Oddy one of the ones that has an optional "Plus One" seat that can go in the center of the second row (I think those are EX or above, 2006 or newer). I have a 2007 Odyssey EX, and I can easily put 3 seats across the middle row - I have three rearfacing convertibles there now, and they're not super small seats either. That just leaves two in the back, which is pretty easy. Even without the PlusOne I think it's going to be possible, but that would give you more options.