I think its probably two different Georges. Summer Rods was the home of Anne Sparkes father Ralph. Inherited by his son Isaac. Isaac and his wife both died young, presumably without having children. John Nicholson is "Gentleman, of Summerrods" in 1827 Durham Gazeteer.
An inscription in Hexham Abbey "In memory of Ralph Sparke Esq of Summerrods, Who died 9th May 1805 aged 65 years. Also of Jane, his wife, who died 6th July 1806 aged 56 years. And also of Isaac Sparke of Summerrods, their son, who died 15th September 1816, aged 23 years. And also of Elizabeth Mary Sparke, his wife, who died 27th March 1819, aged 22 years".
I think John Nicholson married one of Ralph Sparkes daughters and inherited their property at Summerrods that way. There is a marriage of a John Nicholson and Elizabeth Sparke, Corbridge, 6 Nov 1797. Baptism of their daughter Jane 1799 at Durham St. Nicholas, state he was a Quartermaster in the Provisional Northumberland Cavalry, of Corbridge, And his wife Elizabeth Sparke was of ... missing (FreeReg). Baptism of their daughter Mary 1803 Corbridge, state he was a Joiner, of Corbridge Parish and his wife Elizabeth Sparke was of Hexham Parish.
Alan.