Just to be sure, is the tight crank right or left hand threaded? If all is normal, pedals tighten on either crank when turned top toward the front of the bike?
It's possible that the crank is right and somebody reassembled a pair of pedals reversed. (right spindle in left body). Or, if the cranks are truly threaded opposite of normal, and in good shape, then I also suspect that they were made as "captain's" cranks for a crossover drive tandem.
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