Complex sentence: The mastermind of the plot was Agustín de Legazpi; nephew of Lakandula and son-in-law of the sultan of Brunei; and his first cousin was Martin Pangan, the "gobernadorcillo" of Tondo.
Split into simpler sentences: The mastermind of the plot was Agustin de Legazpi; nephew of Lakandula and son-in-law of the sultan of Brunei. His first cousin was Martin Pangan, who was then the "gobernadorcillo" of Tondo.