Complex sentence: During the 18th century this entire range of buildings was, by courtesy of the Pope, the residence of the exiled Stuart dynasty who were resident in Rome and recognised by the Catholic Church as the rightful kings of England.
Split into simpler sentences: During the 18th century this entire range of buildings was, by courtesy of the Pope, the residence of the exiled Stuart dynasty while in exile in Rome. They were recognised by the Catholic Church as the rightful kings of England.