The S-Max isn't the same size as the Sharan. It's a Touran sized motor. The Ford Galaxy is the Sharan equivalent.
I have a Seat Alhambra (with the 2.0 TDI), which is the same again. Mine is a 2007 model, with a current 155k on the clock, and is running sweet, just now. Although I have had to spend some money on it in the last 30k, including head gasket, timing belt, clutch and flywheel, and some suspension refresh. BUT, with that out the way, it does drive well, and should easily go another 50-100k I would think. It may need more bits and pieces along the way though, but it is a high mile, older motor.
Depending on what age of motor you are looking at, The Galaxy, Sharan and Alhambra are all basically the same (from around 1998-2007). Only the Ford changed around 2007, then the Sharan and Alhambra were updated closer to 2010. But they did see updates from the 1.9 TDI to the 2.0 TDI at some stage.
None of them will really have much, if any, boot space with 7 seats up. My Alhambra certainly doesn't. MASSIVE boot space if you only use 5 seats though. They really are designed to comfortably take 7 adults. NOT 7 adults plus luggage though.
I agree with ExoMale here, you don't need a MPV if you need to take 7 people plus luggage. You need a van / minibus.
A great option here, depending on budget, would be a T5 or T6 VW Transporter. You will get 7-8 seats, plus luggage capacity. They are great at holding their value too. So wont depreciate like the MPV's will. But you will need considerably more budget for a vehicle of a similar age as a result.
If moving 7 people, plus luggage is a must, then you're looking at the wrong vehicles.