His wife, Christina, was born on 12th October 1806 to William Hay(~1760) and Christina Seaton(~1765).
I see that Christian, daughter of William Hay and Christian Seaton, was baptised in Barony, Lanarkshire.
What is your evidence for this Christian Hay being the wife of James Boyd (1802-1878)? Their marriage just says that they were both in Cumbernauld, and the 1841 census says that Christian Hay or Boyd was born in Dunbartonshire.
Also they had no son named William, and it was their fourth daughter who was named Christian. They named their first son John and second daughter Jean, which fits the traditional naming pattern. Their first daughter was named Janet and their second son James, suggesting that Christian's parents might have been James and Janet.
Their fourth son was named Joseph. I note with interest that James Hay and Janet Scott had a son named Joseph, born in Cumbernauld in 1799, and I
speculate that Christian Hay, wife of James Boyd (1802-1878) was an unrecorded sister of this Joseph, and daughter of James Hay and Janet Scott.