Complex sentence: Mandarin High School is considered to be a new school for the County of Duval in Jacksonville, Florida; this school has a "sister school" named First Coast High School which shares similar history and ranking status in terms of academic levels in the region.
Split into simpler sentences: Mandarin High School is considered to be a new Duval County school in Jacksonville, Florida. It has a "sister school", First Coast High School, which shares a similar history and ranking status in terms of academic levels in the region.