Stravinsky wrote another version of Petrouchka with two harps, and parts of that don’t work, either. As Elinor says, it’s up to the harpist to edit the part to create the effect that the composer wanted. Read Beatrice Schroeder Rose’s book The Harp In the Orchestra to get more examples of how we adapt standard orchestra parts. For that beginning passage, I just play the top line, and if there’s a 2nd harpist, he or she takes the bottom line. I practiced it with both lines, but it is very tiring and doesn’t make the slightest difference to the overall sound. It’s supposed to be a chaotic scene at a fair, and the harp is buried in the orchestration.