Complex sentence: During his years in New York from 1920 to 1956, he and his sister Mabel, attended many performances and combined their interest in photography and dance by collecting memorabilia including signed photographs of world renowned dancers and autographed ballet slippers.
Split into simpler sentences: During his years in New York from 1920 to 1956, he and his sister Mabel attended many performances. They combined their interests in photography and dance by collecting memorabilia from signed photographs of world renowned dancers to autographed ballet slippers.