If you need a 24x42 for a low, then you’re probably right that the triple is your best option. However, 24/42 is way below what most tandem teams would spec even for hilly terrain.
It’s not hard to get a 2x system well below 1/1 gearing and still have the same high end you have. A low gear of almost .5/1 is pretty unusual on a road bike.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.