I don't know the musical term to use, so let's call one harp the lead the other the background. I'm sure that's the wrong description, but it's all I can think of. Anyway, after you've arranged a song, does it matter who plays lead and who plays background? Do you ever switch back and forth on the same song from one performance to another?
We each learn our own parts and don't trade parts. :) :) We switch off with the melody and accompaniment - even within the same song! We love creating equally intricate parts and making a song our own! :D :D