Complex sentence: After Robert's death in 1769, his widow Isobel continued to live at the house for another 12 years, together with her only son John, who married and had an only son, Edward Dawson (1793--1976).
Split into simpler sentences: After Robert's death in 1769, his widow Isobel continued to live at the house for another 12 years, together with her only son John. John married and had an only son, Edward Dawson (1793--1976).