I fear that you are at risk of making the classic error of assuming that because there is only one person in the records who matches, it must be the right person.
There seem to have been two couples named James Fraser and Margaret Grant, one married 1787 and the other 1808. The children were
Anne 1789
John 1791
James 1794
Pat 1796
Margaret 1798
William 1801
Mary 1804
Sueton 1807
Elspit 1809
Elspit 1810
Mary, 1811
John 1815
Marjory 1819
Alexander 1824
all baptised in the parish of Abernethy and Kincardine, Inverness-shire/Morayshire. I presume that one of the Elspits is the youngest of the first couple and the other is the eldest of the second couple, but I'd need to look at the originals for further clues.
A family at Nethy Bridge in 1841 consists of
James Fraser, 55, blacksmith; Margaret, 55; Janet, 25; Isabella, 24; Marjory, 20; James, 18; William, 13, and Margaret, 11. All born Morayshire except James Sr. Marjory fits the daughter of James Fraser and Margaret Grant, but the others don't, so I personally cannot be 100% certain that this couple is James Fraser and Margaret Grant rather than another James and Margaret Fraser entirely, whose children's baptism records have not survived.
However the census is quite clear that none of this family, or of these families, of James and Margaret Fraser were born in Fife.
I read the birthplace of James Fraser, 30, Superintendent of Police in Gainsborough, Lincolnshire as "Scotland, Fifeshire" not "Falkland, Fifeshire". See attached extract. So assuming that James' age is accurate, he would have been born in 1830/1831 in Fife.
On the other hand, in the 1871 census he says he is 48, which if accurate would suggest a birth in 1822/1823. This would fit with the 18-year-old James in 1841, but not with a birth in Fife. I can't find him or his wife in any later census.
Therefore it is not safe to assume that the blacksmith in Abernethy is the father of the Superintendent of Police.
If I were you, I would forget about the family in Abernethy and Kincardine for the present at least, and see if you can find any police staff records or newspaper articles that might shed further light on the Superintendent of Police.