I think you'll be fine most of the time. Mr. Toad's could be difficult. You can fit 3 across if your two 4 y/o are both pretty small. There is a car out front you can sit in before riding to check. Peter Pan should not be an issue as it fits three pretty well. Dumbo could be another tight one, but again you could try it with the stationary Dumbo first. The Astro Orbiter allows three. Pinocchio, Snow White, and Alice all have two rows so you'll be fine even if you have to take two cars with one adult in each car. Toy Story you can fit three in a row if they're smaller, but someone would not be able to play, same with Buzz. We were told that at Gadgets DD could sit in front of DH and DS, but others have been told no. So that may be up to the CM. Technically they're supposed to allow it as long as the adult is riding with the child. If they all make 40" Big Thunder is an easy one to sit three across and Splash isn't an issue since you sit single file in the log. Space would be another where they might let the six year old sit in front of you, and they may not. But that may be a bit too intense for your 4 y/o anyway. I can't think of anything else where the rows won't allow for two kids and one adult to sit.
We just had our third so this is our future. Fortunately, by the time our youngest is beyond lap sitting or squeezing in our oldest will be seven. But still, she may not want to sit alone at seven, so I hope we'll be able to squeeze together for several years.
