Hi Lynn
Robert BLAIR & Elizabeth McGILL married 1874 in Irvine according to IGI.
This may be them on C1881 - the most likely couple I found in Ayr. Unfortunately, none of the children were born early enough to make it onto IGI - the marriage only just squeezed in

There is a son William which may be your William McGill BLAIR. The connection is helped by Elizabeth on the Census having been born in Irvine, and the first child too , as this is where they married, probably in her parish.
Cheers
Anne
Dwelling: 141 High Row
Census Place: Auckinleck, Ayr, Scotland
Source: FHL Film 0203588 GRO Ref Volume 577 EnumDist 4 Page 17
Marr Age Sex Birthplace
Robert BLAIR M 25 M Coylton, Ayr, Scotland
Rel: Head
Occ: Iron Miner
Elizabeth BLAIR M 24 F Irvine, Ayr, Scotland
Rel: Wife
Alexander BLAIR 5 M Irvine, Ayr, Scotland
Rel: Son
Occ: Scholar
William BLAIR 3 M Auchinleck, Ayr, Scotland
Rel: Son
Annabella BLAIR 1 F Auchinleck, Ayr, Scotland
Rel: Dau
John SMITH U 23 M Castle Douglas, Kirkcudbright, Scotland
Rel: Lodger
Occ: Farm Serv