Complex sentence: Thomas was the only son of Richard Rosewell (c.1588-1640) of Dunkerton, gentleman, and Grace Melborn and the 2nd great grandson of William Rosewell of Dunkerton (died 1568).
Split into simpler sentences: Thomas was the only son of Richard Rosewell (c.1588-1640) of Dunkerton, gentleman, and Grace Melborn. He was the 2nd great grandson of William Rosewell of Dunkerton (died 1568).