George Waddell (Elizabeth Shanks 1826/ Margaret Gillespie 1852) was born 1801, son of John Waddell/ Agnes Russell. This is confirmed from his death certificate. I found a John Waddell/ Agnes Russell married 1826, New Monkland. So there had to be another John Waddell/ Agnes Russell.
Yes, there were at least two couples with the same names, but they are easy enough to sort out. The John W who married the later Agnes Russell in 1826 was the son of John W and Janet Shanks. He died in 1869. I do not know who his grandfather was.
Does anyone have information on George Waddell’s grandparents (ie John Waddell’s parents)?
I think that John W, husband of the earlier Agnes Russell and father of George Waddell of Gain, is the one who died in 1847 and is buried in Whitburn kirkyard. Unfortunately I don't have the Whitbun MI handy, but
(1) his age at death is an exact match for the son of Archibald W and Janet Nisbet, who was born at Leadloch on 29 December 1762 and
(2) his eldest son was Archibald and his second daughter Janet. Also Agnes Russell's parents were Robert Russell and Elizabeth Walker, and John W and Agnes R named their eldest daughter Elizabeth and their second son Robert and
(3) John W was buried in Whitburn, rather than in Bathgate, where several of their family were baptised, or Muiravonside, where they later lived, so presumably had a family connection to that area.
So I think that the parents of John W, husband of the earlier Agnes R, were probably Archibald W and Janet Nisbet. Unfortunately, I can't find any evidence to prove this, and I can't find any information to fit this Archibald W into the main Holehouseburn/Leadloch family.