Lars Osa was married twice. In 1891 he married Hermine Bernhoft (1865–1929), an author of children's books. In 1944 he married Bertha Sivertsen (1883–1968). He was the father of folk musician Sigbjørn Bernhoft Osa (1910–1990). Sigbjørn Bernhoft Osa Store norske leksikon
