A few things. According to William's burial on the Cprdb database he was 72 when he died in 1842 which gives him a birth year of c1770. From the same database Frances died in 1851 aged 69.
In the 1841 Census
HO107/98/21/f7
Sandiway, Weaverham
William Gaff 60(?) Independent
Fanny Gaff 55
Robert Gaff 20
Fanny Gaff 14
Thomas Whitlow 75 Ag Lab
Jemima Whitlow 74
All born Cheshire
Thomas Whitlow died Sandiway in 1845 aged 83. I can't find a death for Jemima.
I have also found another child born to illiam and Fanny, bapised Whitegate 1804, a son, William.
Have not been able to find a birth/baptism for William so far.
Emeltom