There is this family in 1861 census in Walker, Newcastle.
Patrick Duffy, 30, Bricklayer, b. Sligo, Ireland,
Susan Duffy, wife, 28, b. Derry, Ireland
Margaret Duffy. dau, 8, b. Glasgow.
Daniel Duffy, son, 6, b. Glasgow
John Duffy, son, 4, b. Glasgow
Thomas Duffy, son, 2, b. Newcastle
Susan Duffy, 1 wk, b. Walker
Mothers maiden name for Thomas on the GRO website is Kain, for Susan (Susanna) its Kane. Baptism for Thomas on Familysearch is 11 Nov 1858, Newcastle, parents Patrick Duffy and Anna nee Kane.
Cant find them in 1871, but then there is this marriage in South Shields, 17 April 1876.
Neil Ferguson and Susanna Duffy, maiden name Kane.
So that could be the widowed Susan Duffy from from 1861 marrying Neil Ferguson Snr from earlier posts.
Neil Ferguson Jnr, born Sunderland 1872 has mothers maiden name Cain. So unless the Cain/Kane surname is a big coincidence, that would make the Thomas Duffy from earlier posts a half brother to Neil Ferguson Jnr. Birth is before Neil Ferguson married Susan but people sometimes told marital fibs.
The fact that Thomas Duffy has an older brother called Daniel Duffy might be significant.
One small problem with the Daniel Jackson birth, 21 May 1878, is that on the 1939 register Daniel Duffy gives his date of birth as 2 Sep 1877. But perhaps he didn't know when he was born since everything else about Daniel Jackson seems to fit.
Alan.