Checking the 1881 census for a family that fits your description draws a blank (or at least I did

)
There is one possibility for Elizabeth (but it muddies the waters quite a bit)
Dwelling: 42 Comley Park Street, Glasgow
Robert MC MILLAN Head of Household, Age 20 Slater to trade
his wife Maggie MC MILLAN, age 21 and son William age 1 born Glasgow
BoardersJane MC LAREN age 23 born Skelmorlie in Ayr
Rel: Boarder
Occ: Formerly Dressmaker
Lizzie MC LAREN, age 1 born Paisley
Rel: Boarder
If this is your family there is no trace of Duncan