Complex sentence: He was a nephew of Sir Gilbert Heathcote, 1st Baronet, Governor of the Bank of England and the brother of Caleb Heathcote, who served as Mayor of New York City.
Split into simpler sentences: He was a nephew of Sir Gilbert Heathcote, 1st Baronet, Governor of the Bank of England. His brother Caleb Heathcote served as Mayor of New York City.