The first trip to disney, our youngest was 7 weeks, the other two were almost 2, and almost 3. The baby was so easy! We would wake up in the morning, and put her in a sling, or bjorn (depending on who had her), and take her off to feed and change, but she spent the whole trip pretty much attached to one of us). Thankfully we went in late November, when it was not really hot (although we did have two over 90 degree days!!).
Most rides we did not even have to take her out of the carrier. We had a full stoller, I do not like the snap and go, I do not like to keep my babies in the carseat other than in the car (personaly opinion though). I like the full size, we could change her laying down in it, and the few times she was in it she could stretch out.
As for night time, my almost 2 year old took the pack and play, the almost 3 year old slept with daddy, and I slept with the baby. She would wake up to eat, and if she pooped I would change her in the dark (keep everything close, but I think by that point she was going all night in the same diaper, I am one of those once they don't poop every feeding leave them in the same diaper until they wake up in the am people). She never woke the others up, and since we nursed, I slept through most feedings as well.
With all those extra hands, it should be a breeze! I loved traveling with my little ones, they are so easy to bring along.
We nursed everywhere, and changed in the stoller where needed to. That trip we did not even visit a baby station, although, they are great to use if you need to. Plus the sell indvidual baby things if needed!
Have a great time, and enjoy it, it will be nice for your older one since the baby will be so easy!