Complex sentence: His father then married Martha, who was the widow of Charles Pope, her cousin and son of William and Cynthia Pope, and Alexander Pope Humphrey became the half-brother of Edward William Cornelius Humphrey.
Split into simpler sentences: His father then married Martha, who was the widow of Charles Pope, her cousin and son of William and Cynthia Pope. Hence, Alexander Pope Humphrey was the half-brother of Edward William Cornelius Humphrey.