I looked at a sit and stand stroller when I was expecting my second child.
Teh sit and stand says the older child should be 2.5 - my kids are only 18 months apart. so I didnt get the sit and stand.
At 2.5 my older child would have been able to sit on the little bench nicely.. at 18 months she would not have sat and it would have been dangerous.
If the stroller that you need is very expensive.. you might be better off to buy a used Graco dou glider and a used graceo infant carrier. you could get it on craigslist fairly cheap.
I havea graco duo glider and it was so perfect when I had a newborn.. the back seat lays down totally flat and you can put the foot rest up so it is a little bed forthe newborn.
However now that I have a 3 year old and a 18 month old.. I hate the graco double stroller... It is very heavy...(of course the kids are heavier too)
I keep thinking about buying a double umbrella stroller. Just something light to move 2 kids areound easily. For short distances Ihave them walk holding hands. But it has only been the last month that they have both cooperated towalk nicely and safely.