It is interesting that one of the major tandem builders (located in Cal, used to run small tours and now runs 100+ tours on boats, builds off size head tubes, and everything in his wheelhouse is the best, but has great web site) used to strongly advocate 26" wheels and no lateral tubes, but now doesn't even feature 26" wheels as a good choice.
26" wheels are a great choice for a tandem. And most of us aren't racers.
There....said my piece. And yes, we had a 26" wheeled tandem for our first. Now have two sets of 700 wheels for my current tandem.
__________________