So much depends on your family & park style. We're taking our first family Disney trip in early December & will be renting a side by side dbl stroller for our children, who will be 6 & 4 at trip time. We have a sit & stand style stroller at home (that we love) but we want the option for both seats to recline, which is why we're willing to push the double. We anticipate our 2 kiddos using the stroller for quick cat naps or to get into some shade, and we will put them both in it if a crowd level is high and we don't want to worry about losing sight of them.
I mean this respectfully, but I don't understand why people chime in to say that certain ages shouldn't be in strollers. To my way of thinking, all families are different. Could be that one family's oldest child is the slowest and will drag down the pace all the time if they don't have a stroller. Could be that having a stroller helps protect Dad's back from carrying a kiddo everywhere. Could be that using a stroller cuts down on kid whining at Disney, even though they never use one at home. Could be that having a double stroller means no jealousy from a slightly older kid about how come the younger one gets to ride everywhere. Frankly, the bottom line for me is that if I do what I can to keep my family running smoothly, then we don't affect other guests negatively either. I've read a lot of posts on these forums about people seeing meltdowns from kids and how sometimes that affects their own experience, so I don't understand why anyone would NOT want a family to ease their trip in any way they could.
By the way - my sister has 3 kiddos (6, 4 and not yet 2) and she's going to rent a double stroller and bring a folding umbrella stroller that she will keep bungee-corded to the larger stroller. Then if she needs both strollers, she'll unfold it. So if you want to take 2 umbrella strollers, just fold one up & bungee strap it to the other one when one is not in use.