I went earlier in the summer with my parents and had a 2 BR at VWL which I paid for on a rewards type card. They in turn paid for a major meal for my wife and 3 kids and bought all of our tickets for 2 days in the parks.
The only issue I think a lot of other people here have mentioned in the past is the seperate v. together time when you have multiple families on a trip. If it's not clear, sometimes people think that every waking moment must be spent together. Everyone has to be ready to go eat, go to the parks, leave the park, shower, sleep, etc. I know some people don't mind but I think most people like some seperate time and it sometimes causes bad things to happen. Be up front about everything I guess is the point.