My b/g twins are 7 months old now. I agree that for the beginning you will need a Double Snap and Go. A used one would work fine but if you can't find used, they are on Target.com.
Once they outgrow the Double SNG, you will need another stroller. Papa Joe mentioned some great al-terrain strollers like the Mountain Buggy Urban Double and the Valco, but don't forget the Adventure Buggy Company Twin Everest. It will accommodate a toddler seat on top OR a double toddler seat. Another excellent stroller.
But you might not even need one of those. You might only need something like a double umbrella stroller (like a Maclaren, etc). If I were you, I'd wait to buy until you need it. Stroller change so often that they are constantly adding new features. There might be something better out there by the time you need it (this has happend to me twice now).
As for carriers, I'd post on that particular board. There are a lot of moms there who are very knowledgeable. There is only one wrap that I know of that could accommodate twins (the Moby Wrap) which I have and love, but I don't know much about the other ones. hth
ETA- the Moby Wrap will only accommodate twins for the first 6 weeks for fullterm twins maybe longer for preemies. Then you can only carry one at a time.
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