What has worked best for you and why?

I rarely go out without both kids, and I have more than two adults the majority of the time.

Thnks for your inputs.

Cathy

My SIL has the kind of van you have, where you climb between the captains chairs. My van is the older kind with the bench in the middle, so you get to the back seat thru the side.

1) The children's safety is paramount
2) The trouble an adult goes thru to sit in the back seat is nothing compared to the trouble of buckling a cranky toddler into the back seat.

If it appears to be too much trouble, or if the adult passengers are very tall or would be uncomfortable in the back, we take two cars :-)

You should have seen us on our last car trip in a Toyota Sienna, with a 6-month old, 3-year-old, 4-year-old, 4 adults, enough suitcases for all present, and diaper bag/formula/etc for the baby. We were in the car for 3 and a half hours straight.
Next time we take two vehicles :-)

Usually I put the booster seat for 5 y/o in capt. chair behind the front passenger. I put DD 2 y/o in her seat in the very back behind the driver. My 8 y/o will sit in the seat either behind the driver (almost always me) or in the back to keep DD company. It's easy to get everyone in that way because w/ the driver middle seat w/out car seat I can flip it up and say "all aboard" and they can all get in on their own and in their seats. I can easy reach DD to buckle her in the back with the seat flipped up. In the booster, DS can reach his belt and hand it to me to click in place, or I can reach him easily by turning around from the driver's seat.

With this set up I can add DH to the front, of course. But I can still add an adult behind the driver and make DS 8 sit in the back. Another small adult could even sit in the middle back and have the leg room of the isle. Or if another mom sits in the front with me, there is still the seat behind the driver to add a car seat. It just give me the most flexability. People think I'm nuts putting the youngest in the back, but it works for us. Luckily DD doesn't mind the back.

We have 8 and 12 hour drives to see either set of grandparents. This arrangment also works well for that because either DS 8 or myself or DH can get through the isle to the back to entertain or help DD in the back.
In early June-ish I'll have #4. I'm still working on that plan! I don't remember what I did the last time I had a carrier, toddler and booster seat in there. I think I had the carrier in the passenger middle so I could turn and see the baby. Then I put both boys in booster and toddler seats in the back on either side. That way I still had that driver side middle empty and could flip it forward to load the back. At their ages, they could climb in on their own, I just had to reach back to buckle them.

Hope my experiences help. I can tell you that it is a constant quest as their sizes and needs change to find the perfect arrangement.