Complex sentence: He was born in Sumner, Illinois, the younger brother of Walter and Lester Melrose who set up the Melrose Brothers Music Company in Chicago in 1918, and went on to become leading figures in the Chicago blues and jazz scene of the 1920s and 1930s.
Split into simpler sentences: He was born in Sumner, Illinois and was the younger brother of Walter and Lester Melrose, who had set up the Melrose Brothers Music Company in Chicago, in 1918. He became one of the leading figures in the Chicago blues and jazz scene of the 1920s and 1930s.