I've been scouring auto rental sites and while many vehicles will fit 4 adults, few claim to be able to handle that many people and more than 2 large suitcases. We will all be traveling with approx. 22" (or smaller) carry on suitcases and small day bags. What European models have cargo areas which will accommodate all of us and our gear? I'd be interested to see if any users have had direct experience with such a load in wee European cars.
One to eliminate is my favorite: Fiat 500L, very comfortable for four passengers but tight for that much luggage, unless day bags stay inside the passenger area.
You've got to go a "mid size" car to handle four 22" rolling bags. But that's all the trunks will handle. The day bags would have to go in the back seat. Go any larger car or small van and the price rises exponentially.
For what it's worth, on our last three trips, our family of four rented a Class D Large Compact Automatic (Vauxhall Astra or similar) from Enterprise, a Class E/Intermediate automatic (Ford Mondeo or similar) from Enterprise, and an Economy Kia Cee'd automatic from Budget. In each case, we were able to fit four rolling softside carry-on suitcases and four small day bags in the boot.
Our solution was to rent a station wagon. They are very popular in Europe for normal families and also quite widely available as rental cars. A station wagon will offer you enough seating and luggage capacity at a price that's still affordable. Vans go up in price exponentially.
I don't remember what Class it was, but many years ago we rented a Renault Scenic in France because there were 4 of us, and it was very spacious. I prefer to drive as small a car as possible, but despite the Scenic being roomy, it handled like a normal size car.