We're close to your size - I'm about 6' 3" and my wife is about 5' 3" -- and we ride a Burley Tosa medium. We could ride a large, which would defintely fit me better, but the stoker seat would be all the way down for her -- which isn't a problem if you're not using a suspension post.

We also looked at the Cannondales as OHB suggested and they have a good fit for the height difference you have.