Voices for guitar

I've been looking at this simple arrangement of Silent Night that classical guitarist Douglas Niedt has generously shared for free . I'm pretty new to reading sheet music, but I believe that even though this is written for solo guitar, one might consider it to consist of two "voices". The lower notes would be considered one of the voices ("harmony"?) and the higher notes a separate voice ("melody"). Does this seem correct? Regardless, my goal is to create a new arrangement where my idea of the harmony voice would be for classical guitar (my instrument) while the melody voice would be for soprano saxophone (my wife's instrument). Of course on that arrangement, there would be two staves, one for each instrument.