His father Hans Blackwood (second son of William Stewart Hamilton of Grenville Street, Esq) a Director in the Bank of Ireland, married Frances, eldest daughter of Bertrave Mitford of Clontarf, Esq on the 27th April 1835 at Clontarf Church.
Hans Blackwood died on the 27th October 1864 at Hynam Lodge, Bray, County Wicklow aged 55.
Their residence seems to be spelt differently depending on which account you look at with a creditors report in April 1865 spelling it Highram Lodge.
His mother Frances died 28th May 1877 at Highnam.
William Stewart's oldest sister, Frances Eleanor, died on the 5th June 1881 at Highnam. He seems to have had another two sisters, Georgina Sophia (the youngest daughter of Hans Blackwood) who married Charles Edward Stewart on 8th May 1884 and Harriette Isabella Hamilton.
On the 15th November 1877 at Leamington parish church, William Stewart married Mary Isabella third daughter of Colonel Robert George Archibald Hamilton Gun Cuninghame of the Wicklow Artillery(what a name!!) of Coolawinna,Mount Kennedy, County Wicklow.
Their first child, a daughter, was still born on 14th May 1880 at Mount Kennedy. Wicklow.
William Stewart had at least two sons, Archibald Hans Blackwood Hamilton (late Welch Regiment) of Longford Terrace, Bray, He was to marry Gwendoline Crackenthorpe Perks, of Stanley-avenue, Norwich, on the 22nd November 1911 at St Andrew's Church, Norwich. His brother W. Hamilton was his best man
Hope this helps.