Complex sentence: Guterre and his son, Payo Guterres were decisive captains during those years and other sources claim that Guterre Pelayo was the third grandson of Fruela II of León.
Split into simpler sentences: Guterre and his son, Payo Guterres, were decisive captains during those years. Other sources claim that Guterre Pelayo was the third grandson of Fruela II of León.