I have three kids and five strollers. My kids are now 5, 2 1/2, and 3 months. When I take more than one kid with me, I have to use the sit-and-stand. I hate this stroller, but it is the best option for me right now, since the baby is still in the car seat carrier.
I have the Baby Trend sit-and-stand. I only paid $99 for it, but you get what you pay for. It is rickety, very hard to manuever, and the storage basket is hard to access. But it gets the job done and it isn't too heavy. My kids are very small. My 5 year old and 2 1/2 year old can actually share the tiny jump seat! It's nice to be able to have all three kids contained in one stroller. I only use this stroller in a mall or on very even pavement. It's not good for neighborhood walks.
If I had to do it all over again, I would probably get the Joovy sit-and-stand. It is a little easier to maneuver, and it isn't quite as long, so if you want to use it for just one kid, it's not much bigger than a single stroller. And don't bother paying extra for the ultra-light version. I tried the regular and ultra-lights side by side. The main reason for the weight difference is the canopy material. I usually remove the canopy anyway, so it's no real benefit.
Since your younger child is already one year old, I'm not sure that a sit-and-stand is something you will like. The seats don't recline much at all, so if he's not in a car seat carrier, he probably won't be able to get a very comfortable nap. Maybe look at a Phil and Ted's mountain buggy?