Here is a bit of info about William, I will have to dig through some papers for his parents and siblings and will get back to you.
Cheers Pongo
The first member of the family to set foot in Australia was:
William Stewart (1769-1854)
Born at Dounreay, in Caithness, Scotland, William joined the army in 1796 and became Colonel of the Third Regiment of Foot. From 1825 to 1827, he served as Lieutenant-Governor of New South Wales. In 1827, he was given a grant of land at Mount Pleasant, near Bathurst. The same year he went to India with his regiment and was appointed Major-General. He returned to Mount Pleasant in 1832 where he remained until his death in 1854.
While in Canada in 1814 he married Ann Sylvia Wolfe by whom he had the following children:
Caroline Madelaine - Born Montreal, Canada, in 1815. She married, firstly, Captain Donald Stewart, a cousin, and after he was killed in action in 1844, she came back to Mount Pleasant and married Charles Henry Green, at one time Commissioner for the Western Gold Fields. In 1855, she and her husband went to Queensland where they settled on the Darling Downs. She had no children and the date of her death is not known.
Elizabeth - Born in Saint Pol, France, in 1817 where her father was stationed after Waterloo as part of the Allied Army of Occupation. She married the Reverend Mr K.D. Smythe, Presbyterian minister at Bathurst. She and her husband went to Scotland in 1863 where she died in 1908.
Ann - a twin of Elizabeth who died at the age of 18 months.
Letitia - Born in Edinburgh in 1820. She married a Mr David Kennedy, manager of a bank at Bathurst. They had three sons and Letitia died in 1894.
William - Born in 1822, he died at Strath of Bylster, near Wick, Caithness, in 1829.
James Horne - Born in Edinburgh in 1825. He was named after his father's uncle, James Horne of Stirkoke, Caithness. He came to Australia in 1834 with his mother and the other children when they rejoined William at Mount Pleasant. James was educated at the Australian College in Sydney and in 1855 married Harriet Eliza Boyce (1839-1923), the daughter of the Reverend Mr William Boyce of Sydney. Harriet and James had five children.