Hmmm. FS has a note of a family in the 1861 census in Hartlepool consisting of Ann Hunt, 38; William Hunt, 9; Hannah Hunt, 7; Dorothe Hunt, 5; Eliza Hunt, 3; Emma Hunt, 5.
The GRO has births of Mary Ann Hunt in 1847 in Sedgfield, William Hunt in 1851, Hannah Hunt in 1852, Emma Hunt in 1855 and Martha Hunt in 1857, all with mother's surname Dennis or Dinnis or Dinnes or similar.
In 1841 there's a family with John Dennis, 50; Hannah Dennis, 50, John Dennis, 30, Matthew Dennis, 15; Ann Dennis, 20; Rebecca Dennis, 3.
So is Rebecca the illegitimate daughter of Ann Dennis, who married John Hunt in 1845? If so, it demolishes my idea that maybe the Hunt siblings were Duncan's half siblings on his mother's side, his father having died.
Back to the drawing board, I think.