Eileen Smith has provided some info that seems to sink my surmise that Wm 1827 s/o Philip & Mary was husband of Selina.
She sent me a press cutting dated March 14th 1860
which reads:

Amongst the persons lost on the HUGARIAN Montreal
steamship wrecked on the 24th February 1860 at Sable
Island were 3 young men of the Isle of Man. WILLIAM
CAIN, 4th Officer, aged 32 years son of Philip Cain,
late of the Saddle Inn, William Quine 27 and William
Nelson, 20 seamen.

So if Phillip's Wm 1827 died in 1860 he couldn't be the Wm who fathered the last two children and who appeared in the 1871 census

Anthony Dickinson is her ancestor. He was s/o Joseph Dickinson/Mary Tyson and brother of Sarah. IGI has his parents listed incorrectly.
Thanks so much, Eileen.

Back to the drawing board!
Donna