I was worried about this too. Back when we first took our twins (now 4.5 yrs) to Disneyworld (for a week), they were a few months shy of being 3, and, my son especially, would cry himself to sleep (even now, it still happens occasionally). We had taken them on vacation before, but that was the first time in that kind of situation, so I was nervous. Honestly, we needn't be worried. Disneyworld has a way of wiping out kids. You would think that everyone being in the same room would making bedtime a bit of a zoo, but at DW, they have a tendency just to collapse.
However, I can still understand being worried. I know that in terms of soundproofing, the Unofficial Guide rates the values as some of the highest. I've heard, that you need to keep your bathroom door shut. You should also keep to the twins' schedule as much as possible. Also, even if you don't use music to help them fall asleep at home, I found, that one vacation, classical music was a great way to drown out background noise and help them settle down.
GL.