I'd say ask your DH to figure out the arrangement so he can really see why you want your van.
Have you tried loading through the cargo area? I was really opposed to it when I was accustomed to loading everyone through one door, like a van. Turns out it's kinda handy using the cargo area as a holding tank! I keep a double jogging stroller stood up on one side and the remaining space is open (except a pile of blankets and cargo bags/cooler bags that they can just step on). I send the third row kids in through the cargo doors and shut them in there--no interior handles means they can't fall out (hint:it also means you can shut yourself in accidentally...) then I take the second row kiddos around to their door(s) and buckle them while the third row kids either good around or climb into their seats. Then I go back and climb in the cargo area to buckle the rear facers in the third row. You can reach the third row forward facers from the second row without flipping/sliding the seat if you stand on the door step and lean over the seat back of the second row, provided the seat has a rear facing seat or a backless booster. Also in my set up my 5 yo in the third row can buckle herself (FR85) but can't UNbuckle. In front of her is a recaro Prosport so I can't reach over the seat but I CAN reach just my arm back there to UNbuckle her. If she struggles to buckle though I can reach her from the opposite side of the car by leaning way over the second row since there aremRFers in both middle and driver's side outboard. I also sometimes buckle my 3 yo from standing in that spot (drivers side 2nd row door step) and she is RFing in a Radian w/AA in 3rd row center. Also I send all the third row kids up and over through that same door whenever we can't access the back cargo area--groceries or whatever, or bikes/quad stroller on the hitch.
And that's another idea for you;have you do sidered a 4 seat stroller so you can do that walk for drop off? As long as your side walks are cleared it should be doable in all but the worst cold rainy or stormy days. Check Craigslist. Mine is a quad runabout and I absolutely loved it whenever we had 4 babies and toddlers. Or could the four year old walk? Maybe with a harness? Then you could put one baby on your back and two in your stroller. Plus the fresh air and excersize might put everyone in a better mood and break up the day in a more pleasant way.
BTW the car I referenced above is a suburban. 1998 though so I can't help with what particular seats would work with yours, sorry. But I feel your pain, big time.
