Could you put the baby in the backseat with 4yr old, and 2yr in the middle, in the middle? It would mean noone had to try and get around the baby seat in the middle row, because it would be an upright car seat, not laying down?
We are trying to sort our car out too!!!

We'll have a 2yr, 3yr and 4 yr, and newborn.. so 4 car seats!! Plus the 3 big kids.....

We are putting the baby, 2yr and 3 yr across the back seat.. and the 4 yr booster in the middle row, in the middle.. so when we have 2 big kids as well, they just jump in each side...

I use a sling, so will sling bubba, put all the kids in, then baby last.... and when getting out, baby first in sling, then the others....

Its all sounding so complicated... I think I need the big old van back... we wont even fit in this car now, so we'll have to take two when we all go somewhere together!!