Complex sentence: John Brownlow had married an heiress but was childless; he was attached to his only two blood relations, a great-nephew, also called John Brownlow, and a great-niece, Alice Sherard.
Split into simpler sentences: John Brownlow had married an heiress but was childless. He became attached to two of his more distant blood relations: a great-nephew, also called John Brownlow, and a great-niece, Alice Sherard.