Well there is this interesting looking family from 1861 Scotland. Perhaps not quite where you expected but still worth investigating I think! Note the spelling of Macniel.
Reg #: 373
Reg dist: Little Dunkeld
Civil parish: Little Dunkeld
County: Perthshire
Address: Milton Of Kinloch
Household consists of:
John Macniel age 42, head, b. Saltcoats, Ayrshire, Occ: Game Keeper
Mary Macniel age 42, wife, b. Saltcoats, Ayrshire
William Macniel age 16, son, b. Dunoon, Argyleshire, Occ: Under Game Keeper
Jane Macniel age 13, dau, b. Dunoon, Argyleshire, Scholar
John Macniel age 6, son, b. Dunoon, Argyleshire
You'll find the 1861 image indexed on SP as:
1861 MACNIEL JOHN LITTLE DUNKELD PERTH
Jumping backward to 1851 the family is right there in Dunoon and John apparently has a big sister named Mary b. in Saltcoats about 1838.
Civil parish: Dunoon and Kilmun
County: Argyll
Address: Steading
John Mcneil age 34
Mary Mcneil age 32
Mary Mcneil age 13
William Mcneil age 6
Jane Mcneil age 3
Does this fit with what you know of the family?
Best wishes
Jean