Ooh, what about a Co-Motion model with the "periscope" rear seat post? We have one in a size Large that fits my 6'2" hubby on the front and anyone from like 3'6" - 6'2" on the back. It's primarily our 10 year old's bike--this way we can all get out for rides together. You guys would probably want the smaller size (medium?).

This is the one we have. It can be made with couplers, too.