Original sentence: The songs are not unified in the work: the three songs of Ellen are piano songs for a woman's voice, the songs of Norman and the Count of Douglas ones were foreseen for the baritone Johann Michael Vogl
Edited sentence: The songs are not intended for a single performer: the three songs of Ellen are piano songs for a woman's voice, the songs for Norman and the Count of Douglas ones were planned for the baritone Johann Michael Vogl