Hi Andy
you would be better renting a 9 seater as most 7 seaters only have space for 1 or 2 pieces of luggage as seat 6 and 7 tend to be under the boot floor, and when you pull them out to use, you will lose all your lovely boot space.
if there is more than 1 driver you will be a lot cheaper renting 2 cars than 1 large one
we are paying 188e for a Vx Zafira for 13 days in april with Firefly and they were the cheapest around for our dates
we also looked at a 9 seater but it was only the big boys who had them we were quoted over 600e for a merc vito 9 seater for the same period