Complex sentence: The estate at Hamsterley was given, in 1762, by Sir John Swinburne Bt to his younger brother Henry Swinburne, who in 1769 carried out substantial alterations to the then existing house to create the present two storey, four bayed castellated Gothic style mansion.
Split into simpler sentences: The estate at Hamsterley was given, in 1762, by Sir John Swinburne Bt to his younger brother Henry Swinburne. In 1769, Henry carried out substantial alterations to the then existing house to create the present two story, four bayed castellated Gothic style mansion.