Complex sentence: Sethos is initially presented as a rival to Emerson for Amelia's affections, but becomes an important part of the Emerson's large circle of friends, allies, and acquaintances in later books, as it is dicovered that Sethos is Emerson's half-brother.
Split into simpler sentences: Sethos is initially presented as a rival to Emerson for Amelia's affections, but becomes an important part of the Emerson's large circle of friends, allies, and acquaintances in later books. As it is dicovered that Sethos is Emerson's half-brother.