Complex sentence: After Lenox's death, his son Robert Lenox Kennedy succeeded him; who would serve for seven years before being replaced by John S. Kennedy, who would serve until the merging of the libraries in 1895.
Split into simpler sentences: After Lenox's death, his son Robert Lenox Kennedy succeeded him. After Robert Kennedy's death, John S. Kennedy took his place and would serve until the merging of the libraries in 1895.