Would this vehicle accommodate four adults plus their four large suitcases and carry-on items? Is there space behind the third row of seats, so that if they are folded down (and/or we put suitcases right on the seats) there would be enough storage space?

Loads room, you can fold up the rear seats with enough room or take the seats out and the centre one if you dont need it.
We took the rear bench out for suitcases for five of us and food and games for a caravan holiday
jay