Sorry, I didn't have time to look things up yesterday.
I'm not sure if the following is the correct family as I could find no Peter Duncans with a wife called Agnes:
1841 Clathy, Perthshire Findo Gask; ED: 1; Page: 6; Line: 530
Peter Duncan, 45, Farmer, bc 1796 [but this is the 1841 census where ages were out about 5yrs
Ann Duncan, 45, bc 1796, Scotland
There were youngsters with them with surname of Scharton [not sure this is correct], Mary 14 and Jean 9; Matilda Seaton, 19; all born Scotland. No occupations beside any of them so perhaps they were relatives? The others on the page were all Ag Labs.
* have just found a Matilda Seaton b, 1821, Dunoon; parents James Seaton and Catherine McIsaac, the latter was an Ag Lab with the Duncans in 1841.
1851 Clathy Village Findo Gask; ED: 1; Page: 1; Line: 12
Peter Duncan, 60, Farmer of 16 acres emp., 1 servant, born Gask
Ann Duncan, 58, b. Muirkirk, Ayrshire
Sanson Cook, 19, Agricultural Servant, b Masaty [Madderty?] Perthshire.
1861 Clathy Village Findo Gask; Findo Gask; ED: 1; Page: 15; Line: 6
Ann Duncan, 70, occupation [Findklder]!, bc 1791, Muirkirk, Ayrshire
If Agnes was called Ann then Peter may have died either before the census was taken on the 7th April 1816 or pre- registration
McAra:
I don't see any connection with yours but they all lived around that area of Monzie, Monzievaird as did my McRaw/Gould/Guild, McIntyre ancestors.