Hello Scully,
I think your William Galbraith, married Elizabeth Mackie, 09/Dec/1854. Kilwinning, Ayr.
Also your Margaret Galbreath, was born 29/April/1856. Kilwinning, Ayr.
The family then moved to Paisley, where they had,
Elizabeth Galbreath, born 12/Feb/1858. High Church. Paisley,
William Galbreath, 07/March/1860. High Church, Paisley.
By 1881 your census of the Grants, in Kilwinning, with Mother in Law, Grant. well my census gives her name as Elizabeth Mackie, mother in law, Widow, aged 52 years, born Kilwinning.
This name Mackie, fits in with the marriage above, and the births of Elizabeth, 1858. and William, 1860.
You will find however that the name Galbraith, etc, and Mackie, have various spellings in this family.
Elizabeth Mackie, born about 1830. Kilwinning is out of a large family, but no births for this family on the IGI.
You will have to get the death certificate of Elizabeth Mackie Galbraith, born about 1830 to confirm her parents names.
Regards,
Jonn.