I've used just about every double out there one time or another (I have an obsession with strollers, I admit it).
I can't see pushing more than 80lbs of child (single or double) in any stroller with small wheels like a Maclaren. I have a Mac single and love it but it's a bear to push on rough surfaces with my 50lb 4 year old as the wheels are small. For him, I have the Baby Jogger City (not the City Mini) and thanks to the air-filled larger wheels I can push it with one finger. As the size of the child goes up, the size of the wheels has to go up or you're going to get tired and cranky pushing that much weight around.
If you really need a double for two bigger kids, the BJ City Mini would work but in all honesty I'd seriously consider two BJ City Classics (each with a weight limit of 75lbs.) or two City Minis (weight limit of 50lbs) or a mix of both if you have two adults to push and if renting two singles is in your budget. I had posted the specs of the City Classic on another thread for someone who wanted to know if their tall child would fit and I think I remember it has a butt-to-canopy height of 22 or 24 inches. So when your child is sitting, measure from the surface of what he's sitting on to the top of his head to see how he'd fit.
You can find the specs of the City Mini here under "Let's Go Strolling stroller specs" to get an idea of how your kids would fit, but keep in mind that if you exceed the weight limit you risk damaging the stroller. Granted they're sturdy enough that it would probably take some significant weight to damage them as opposed to the 10lbs or so you're talking about, but it's something to keep in mind.
http://www.letsgostrolling.com/baby-jogger-city-mini-double.html
If your kids will fit and you're willing to push that much weight, the City Mini is an awesome stroller. But it would be easier for the adults and the kids would have more wiggle room if you could swing two City Classic singles.
I don't know of any place near WDW that rents full-size jogging doubles that have higher weight capacities. Worst case, you could just rent a Disney double stroller and see how you like it.
