Sit and Stands are great for small children, but I think your kids are too big. The front seat of our baby trend is too small for my slender 4 y.o. and even when he was 3 his legs were too long for the front. Of course the bigger kid is meant to be in the back (ours converts to a true double stroller with an extra seat that can be removed to the sit and stand platform/jumpseat).
Besides the size constraints, the stroller is very hard to push. If the kids are younger/smaller, I don't think that would be an issue. My stroller also has air tires, which I thought would allow for easier pushing/steering. Not the case, unfortunately.
How about a jogger? That might be easier to push and accomodate older kids.