Hi everyone. Many thanks for all the responses, but I'm afraid, Annie, the William you found isn't cousin William.
Some more details ...
Frederica was 14 years James's junior
- born abt. 1824 in France, d/o Robert de Lisle a Landed Proprietor, and Frederica Mills, and she died at 3 Abercromby Place, Edinburgh on 3 Nov 1859. She is in the 1851 Census with husband James, a Solicitor, Supreme Court. There are no children, but there are two "Visitors" listed that are, more than likely, Frederica's sisters, and a house servant.
James and the children - Frederica junior, Robert, Elizabeth and William were all at 3 Abercromby Place, St Mary, Edinburgh in the 1861 Census. Another daughter Cecelia died in 1859 age under 2
James remarried Anne Helen Rattray on 2 August 1864 and he died just 4 years later on 9 March 1868.
James seemingly ran into difficulties as this extract explains:
EDINBURGH GAZETTE: Friday, May 8, 1868
"NOTICE is Hereby Given that the Lord Ordinary officiating on the Bills has, on considering a Petition by Hugh Paterson & Company, Carpet Manufacturers and Cabinetmakers, South Bridge, Edinburgh, and Hugh Paterson, the sole Individual Partner of the said Company, for Sequestration of the Estates of JAMES NEILSON, Solicitor before the Supreme Courts of Scotland, lately Residing in No. 16, Duke Street, Edinburgh, now deceased, granted warrant for citing
Frederica Margaret Archer Neilson, Robert De Lisle Neilson, and William Charles Neilson, all Residing at No. 16, Duke Street, Edinburgh,
the surviving Children of the said deceased James Neilson, and the tutors and curators of the-said Children, if they any have, for their interest, and Mrs Anna Helen Rattray or Neilson also Residing at No. 16, Duke Street, Edinburgh, Widow of the said deceased James Neilson,—the said, surviving Children and Widow of the said deceased James Neilson being his successors, in terms of the Bankruptcy (Scotland) Act, 1856 ..."
Daughter Elizabeth died in 1865 and, from the above, William was still alive and living in Edinburgh in 1868.
The search goes on
Chiad Fhear