Complex sentence: Armand Edward Blackmar, born in Vermont in 1826, to parents Reuben Harmon and Amanda (Cushman) Blackmar, was, with his brother, Henry, the founder of Blackmar Brothers, a music publishing company.
Split into simpler sentences: Armand Edward Blackmar, was born in Vermont in 1826, to parents Reuben Harmon and Amanda (Cushman) Blackmar. Armand, with his brother, Henry, was the founder of Blackmar Brothers, a music publishing company.