Complex sentence: Cayman Brac High School is a secondary education school that is the only source for secondary education in the "Sister Islands" (Cayman Brac and Little Cayman) of the Cayman Islands.
Split into simpler sentences: Cayman Brac High School is a secondary education school. It is the only source for secondary education in the "Sister Islands" (Cayman Brac and Little Cayman) of the Cayman Islands.