Complex sentence: Upon Said's death in 1856, his realm was divided: his third son, Thuwaini bin Said, became the Sultan of Muscat and Oman; and his sixth son, Sayyid Majid bin Said, became the Sultan of Zanzibar.
Split into simpler sentences: Upon Said's death in 1856, his realm was divided. His third son, Thuwaini bin Said, became the Sultan of Muscat and Oman, and his sixth son, Sayyid Majid bin Said, became the Sultan of Zanzibar.