Hello Averil,

The connection to the Dukes was through John's mother Jane Cain, and grandfather Hugh Cain, although of course Robert may also have been related - as Liz always says, too many Caines!
I wrote:
[1861 census]
"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
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."

Donna wrote:
"Jane Caine who md William Duke 1842 Braddan is d/o Robert Caine/Jane Kissack
She was ch 18 Mar 1810 Braddan

Hugh Caine/Esther Kissack
Hugh Caine is 1st cousin once removed to Jane Caine, common ancestor Wm Caine/Isabel Oates

Hugh Caine 1795s/o Robert Caine/Mgt Quiggen
Robert 1754 s/o Wm Caine/Isabel Oates

Jane Caine 1810 d/o Robert Caine/Jane Kissack
Robert 1771 s/o John Caine/Isabel Key
John 1746 s/o Wm Caine/Isabel Oates
DJD"

If Jane's (1810) elder brother Robert b.1804 was the father of John, he was having a relationship with a close relative 34 years younger than he was, who was only 20 or 21 at the time.

As she was still living at home, hopefully it was unlikely.

Perhaps the two wives Esther and Jane KISSACK were also related.

Sue