I've done some big European journeys with the family. I strongly do not recommend showing up with more people than the room occupancy. The challenge is obvious. When you email ahead to try and get a room type that accommodates 4, the property sees $$$ as they see this request all of the time. I rarely get helped for no extra-charge into a room type I need even as a Plat.
Marriott-ing Europe
I've done a number of things:
-Booked two rooms and cancelled one if I get upgraded ahead
-Paid for a junior suite that allows a room cheaper than two standard rooms
-Paid for a second room (the worst option especially since you may not even use it with younger kids)
-Paid a daily fees on top of a points reservation (Sydney) to get a room type they refused to offer on points.
I don't know if anyone has noticed, but it has not been long since Marriott has added the people count option when booking online and thankfully max allowed is listed in all room details screens.
I think Marriott is better than Hilton in this regard, but this seems like a ripe market to consider places on booking.com and airbnb/homeaway especially for stays of more than 2 or 3 nights.
As mentioned, properties not only have room type issues, but want to charge for extra people (even if they are kids). I believe only the spouse (or one additional person is free) and that is only because the elite programs have this indicated I believe. This seems silly in the US, but is prevalent across the world. Oh, well I guess this is also a problem in Vegas casino resort properties, but not for occupancy issues, for extra charges.
Thankfully, if I had a room type for the right size, I have not had an issue accessing any lounge or free breakfast amenities for my entire party (which is not so straightforward with SPG either).
Rasheed