I would look at Co-motion. For a few more dollars you can get them to custom fit a frame to you.

In regards to climbing and tandems- the thing that makes the most difference is the riders. Tandems will always climb slower than single bikes. Put two fit guys on a tandem and yes they will go. Improving fitness and losing weight off the riders would be the biggest improvement to climbing.

You are going to need a triple crank for climbing. Even a compact it's not going to do it unless you are elite riders.