Complex sentence: The house has had many extensions and changes over the centuries, the final addition being the West Library which was added by the family of Leopold C. D. Jenner who occupied the house in the early 20th century.
Split into simpler sentences: The house has had many extensions and changes over the centuries, the final addition to the manor is the West Library. The library was added by the family of Leopold C. D. Jenner who occupied the house in the early 20th Century.