Complex sentence: The producers wanted to tell the full story of the Cly family, residents of the Navajo Nation in Monument Valley, Utah, who had been the subjects, presented without their own voices, in the silent film "The Navajo Boy".
Split into simpler sentences: The producers wanted to tell the full story of the Cly family, who were residents of the Navajo Nation in Monument Valley, Utah. They had earlier been the subjects in the silent film "The Navajo Boy".