RootsChat.Com

Hello
The ScotlandsPeople references to the 1841 census each refer to 2 pages in a census book which contain up to 50 people.
The Farr reference 050/8/1 has 38 Mackay / McKays and the Dornoch reference 047/12/3 has 26 Mackay / McKays.
The family group of Alexander, Mary and William appears on none of the pages.
The Farr references are all living in Midtown, Farr. The Dornoch ones are in Proncy.
As far as I can tell, FindMyPast 1841 census for Sutherland has no references given, only a 'Schedule' which doesn't exist on the original.
Ancestry does give references, but they differ from the ScP ones in that Ancestry refers to the exact page, and ScP only refers to the odd (left-hand) ones (which each cover the odd one and the right-hand even page). So the William reference in Farr is 50/8/1 on ScP but 50/8/2 on Ancestry.
Good luck in your search for Mackays in Sutherland!
Bill

The transcripts are available on FindMyPast and Ancestry. 

Those references are not making any sense to me, I cannot see them on the FindMyPast transcripts

I am a little confused as to your reference to FindMyPast  .  Scotlands People is the only site with the original copies of Scottish census

Relationships were not included in the 1841 census.

https://www.freecen.org.uk/search_records/5a151bfef4040b9d6e28357d/william-mackquay-1841-midlothian-edinburgh-1809-?locale=en

You can view the original image on Scotlands People at a small cost.

The FindMyPast index reads "Mary Sellars, born 1817, year 1847.
But looking at the original register the column headed "When received and committed by whom" reads 1874. The pages before and after are headed 1874 also.