djct59,
Yes, as you say, the 1841 census has Barbara (Ross) McCulloch, age 70, of Independent Means, born in Sutherland, and a resident of the Durness Manse.
In 1837 Barbara inherited 800 pounds from her late older brother Quartermaster John Ross. The exact wording of the bequest of the five equal 800 pound shares in the will: "... to Donald Ross, now or lately residing at Pictou in Nova Scotia, John Ross residing at Boularderie Island of Cape Breton in North America, both my brothers, and to my sisters Barbara Ross, widow of the late Kenneth McCulloch residing in the Parish of Durness aforesaid and Janet Ross wife of Angus MacLeod farmer in the said Parish of Durness and Donald Ross my nephew son of the deceased William Ross my brother and found lately residing in the Isle of Hoan Parish of Durness aforesaid..."
It is kind of breathtaking how precisely this bequest defines the locations of the family members in 1837. In addition, the last of the Codicils to the will was witnessed in Musselburgh, where QM John lived, in 1836 by John's nephew Hugh MacCulloch.
Those are the two primary points I use to estimate placeholder years of birth and death for Kenneth - the will of QM John and Barbara's residence as a widow at the Manse in the 1841 Census.
If Kenneth died at about 74 years of age and if Barbara was already a widow in 1836 when the Will of QM John was written, then Kenneth's year of birth would be in the early 1760s, which is consistent with his marriage to Barbara in 1788 and also is consistent with his date of birth as preceding the November 1764 start of DPR.
Regarding the MacCulloch offspring, Merran (Marion) MacCulloch married William Morrison on 20 November 1821 at the Durness Manse. I have not yet traced them further. Her sister Joanna I previously noted married Hugh Morrison at the Manse on 7 October 1818, but what I haven't yet mentioned is that they emigrated to Ontario, Canada.
https://www.findagrave.com/memorial/182030523/joanna-morrisonI've not yet put much effort into tracing the MacCulloch brothers beyond Hugh because there is such a massive amount of detail about Hugh I have yet to find the time to assess. See the attached screen shot of Hugh signing a merchant letter to his partner William Hartnell on 8 July 1822 near Santa Barbara, California - "all the way from Cape Wrath"
The last relevant thread here is that Hugh Morrison and Joanna MacCulloch as residents of Leeds County, Ontario, Canada in the 1830s were the Ross cousins who helped Donald Ross and his wife Isobel Calder, crofters on Island Hoan with 10 children, emigrate to Ontario and buy a farm with the proceeds of their one fifth share of the inheritance from QM John.
[wr]