Mark--You got some negative responses so far and I have to agree with them. I think 2 kayaks linked side--by-side would be incrediably difficult to maneuver, even with two expert paddlers. If you want to paddle with your wife, go with a double or even a triple. If you want a stable boat, look into a rowboat. There are some rowboat kits out there that are no more difficult to build than a kayak. One that comes to mind is Pygmy's kit. Platt Manforte at Geodesic Aerolite has a number of interesting ultralight rowboat kits.

The eskimos built doubles and triples, but it's a matter of some dispute why they did. One commonly held theory is the Aluets built them to transport Russian fur traders. In any case, when they need to move two or more people by kayak, they didn't go the catamaran route.