Complex sentence: After his death in 1761, the castle passed to his grand-daughter, Caroline Fitzgerald, who married her cousin Robert King, Viscount Kingsborough and, from 1797,2nd Earl of Kingston.
Split into simpler sentences: After his death in 1761, the castle passed to his grand-daughter, Caroline Fitzgerald. She married her cousin Robert King, Viscount Kingsborough who was, from 1797, the 2nd Earl of Kingston.