Our oldest son is almost 4 and I'm constantly stroller shopping for him because we live in the city, and it gets to be too much walking for him when we're downtown, etc. We have a sit 'n stand, which I don't recommend because it just doesn't steer as well even though the large basket and double cup holders are nice. With the weight of your kids, it would be extremely difficult to maneuver. We also have the Baby Jogger City Mini, which I love! I'm not a jogger at all and bought it because it's relatively light (~20#) for a double stroller, folds up pretty compactly, fits through any single door that meets ADA requirements, both seats recline almost flat and it has great canopies. It's expensive, though, and you have to buy all of the accessories (cup holder, rain shield), and it isn't easy to get to the basket. It can be steered pretty easily with one hand, though. Now that my older son is getting bigger, though, I am noticing that it seems narrow, particularly when he's wearing his winter coat...and he's a pretty lean kid. If your kids don't nap, I think a wagon is a good outdoor option, but not very good for getting around in stores or in and out of elevators.
PS -We ordered our double stroller on amazon and didn't have to pay sales tax or shipping.