About 5 miles west of Helmsdale along the A897 this is small place (3-4) farms called Kilphedir. However, prior to the early part of the 21st C it didn't exist. There have been small farms identified there since the 1600's, none which carried this name and certainly no estates. The Sutherland estates can be found here
https://maps.nls.uk/estates/golspie-loth/graphic-index.htmlAs for William who died in 1832 it was published on the 24th of October 1832 in the Inverness Courier (and other papers of the day).
On the 5th inst., at his residence in the Cross-causeway, Edinburgh, William Sutherland and senior of Kilpheader, in the 81st year of his age. He was said to be the eldest male descendant of the Earls of Sutherland, and enjoyed a small annuity from the present Countess in respect to his illustrious descent.
I can send you a copy of the paper if you wish.
Killipheder on South Uist you can find on most maps going back to the 16thC but difficult to read. This is the best which shows the extent of the holdings
http://maps.nls.uk/view/74400298 If William lived there the mains still seem to exist and you can see it in Google Maps.
Don