Are all of you physically capable of carrying one of the children? You may only need one single. We went when my son was almost 3, and we barely used the stroller because we had 3 adults who could carry him, and he preferred doing that or walking.
Given you choices, I would just take the double. We went when my oldest was 5, and the stroller mostly carried stuff and carried him for a few times (like World Showcase), but he walked most of the time. If you need to separate, can't the 5 year old just walk?
Now this is assuming you are not doing naps in the stroller and aren't commando style.
ETA: I see you made your choice. I have to say, I agree. If there is a place the stroller can't fit, your 5 year old can walk and your 2 year old can probably be carried by someone in the group. Looking after one stroller is a PITB enough for us, 2 would be a headache.