Further to my previous message, this looks like ANOTHER Jane Cain and her son John in the 1861 census [Findmypast], or else her age given in censuses is wildly erratic, or it was a different Jane Cain who married William Duke and had John Cain living with her:

Name Relation Condition Se x Age BirthYear Occupation Disability Where Born CAIN, Hugh Head Married M 67 1794 Flax Draper Ramsey
CAIN, Esther Wife Married F 60 1801 Jurby [KISSACK]
CAIN, Esther Daughter Unmarried F 33 1828 Flax Shreader Jurby
CAIN, Margaret Daughter Unmarried F 28 1833 Flax Spinner England
CAIN, Jane Daughter Unmarried F 22 1839 Flax Spinner Braddan
CAIN, Mira Daughter Unmarried F 19 1842 Flax Reeler Braddan
CAIN, Thomas Son Unmarried M 17 1844 Canvas Weaver Braddan
CAIN, Robert Grandson Unmarried M 15 1846 Flax Heckler Braddan
CAIN, Mary Anne Granddaughter Unmarried F 8 1853 Scholar Braddan
CAIN, John Grandson Unmarried M 2 1859 Braddan
KILPACK, Ellen Boarder Unmarried F 30 1831 Flax Spooler Braddan
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RG number:RG09 Piece:4412 Folio:65 Page:12 Enumeration District:4 Civil Parish:
Address:Cronkbourne Village, Braddan County:Isle of Man

Grandchild: Mary Ann CAIN bapt 10 July 1853 Braddan illeg daur of Margaret Cain.
Grandchild: John CAIN bapt 30 May 1859 Braddan illeg son of Jane Cain.
Daughter: Jane CAIN bapt 17 Dec.1837 Braddan, Father: Hugh CAIN, Mother: Esther KISSACK.

Was the Jane nee Cain who was living with William Duke (and John Cain) an aunt or other relative?

Sue