Re Alan's suggestion of the marriage in South Shields, 17 April 1876 between Neil Ferguson and Susanna Duffy, maiden name Kane.
The newspaper article from November 1877 about Neil Ferguson attacking Mary Ann Jackson says he had engaged her about 6-months earlier to look after his invalid wife - presumably Susanna. A witness was an unnamed step-son of Ferguson.
The article strongly suggests that Mrs Ferguson was still alive, but there is a death registration Q1 1877 Stockton, Susannah Ferguson aged 42.
Oddly it isn't listed on the Middlesbrough Registrars website (Tees Valley Indexes), which was the registration district for Thornaby after 1875, nor is it on the Stockton Registrars website.
So if Susannah had already died, then Mary Ann would likely have been alone in the house with Neil Ferguson and the Duffy boys.