I have all sorts of strollers to fit different needs. I have taken just about every stroller to some type of theme park, including Disney.
I have the same sit-n-stand as baiqi and I HATE it!! Everyone I know who has it, hates it. But to each there own. I just find that it doesn't have enough space underneath, DS4 is always jumping out (no confining him), It doesn't recline enough for DS#2 when he was littler or wants to sleep, & it can be very difficult to steer.
I have a side-by-side double jogger that I LOVE! This is what we took to Disney in May and I found it to be invaluable. It can be a tight squeeze in stores when crowded and a little difficult to get through the gates at MK (no problem anywhere else). I posted some feedback on using it somewhere on this thread if you want to do a search (original thread started by tomkat(?)). However, DS#2 (currently 17 months) doesn't always like to share "his space", usually, but not always. And when he chooses to be a pain about it, everyone in a 5 mile radius notices. So, when DS#3 gets here in just 2 short months, we will be using a double tandem. So, if you get a side-by-side, make sure the kids don't mind always being next to each other.
My personal recommendation would be to rent a double for your DD & DS10 months. It is so much easier than doing two strollers, regardless of the amount of pushers, imo. I've done that before too, and it was a pain. Plus, you'll want the stroller going back and forth from the parks--you and the kids will all be exhausted. And it is a lot of walking for such a little one. Then just rent a single if you find DS7 can't handle the walking.