If my suggestion for Alexander's birth turns out to be correct (you can't be sure until you see his marriage certificate), then this is him and his sister Hellen living with their grandparents in 1881.
Dwelling: Elginshill Census Place: Urquhart, Elgin, Scotland Marr Age Sex Birthplace Alexander COBBAN M 67 M New Spynie, Elgin, Scotland Rel: Head Occ: Farm Serv Unemployed
Hellen COBBAN M 60 F Duffus, Elgin, Scotland Rel: Wife Occ: Farm Serv Wife
Alexander DUNBAR 9 M Elgin, Elgin, Scotland Rel: Gran Son Relative Occ: Scholar
Hellen DUNBAR 8 F Urquhart, Elgin, Scotland Rel: Gran Dau Relative Occ: Scholar