FABULOUS work, Eric! Sometimes it pays to take a chance, to go outside the box. Very good detective work.
It is a great example of the importance of ALL the little details needing to fit. How easy it is to say well I've got 2 out of 3 so this must be it.

The info in my database agrees with Eric's lineage of this Cain(e) line.
John Caine/Ann Gawne
Monumental Inscription Rushen Old Yard and 1869 Yard
#C2:
In loving memory IHS John Cain of Port St Mary who died November 17th 1896 aged 72 years.
Also of Ann (Gawne) wife of the above who died March 30th 1879 aged 56 years.
Also of Thomas their son who died August 9th 1884 aged 28 years.
At rest also of Martha their daughter who died Nov 27th 1913 aged 61 years.

The above Martha was ch 25 Jan 1852 Malew. She apparently never married. She is with her fa in 1881
1881 Rushen
5, 1, 4, CAIN, John, Laghan, Head, Widower, 56, Farm Labourer, Malew
5, 1, 4, CAIN, Martha, Laghan, Daughter, Unmarried, 27, Gen Servant, P.StMary
5, 1, 4, CAIN, Thomas, Laghan, Son, Unmarried, 24, Masons Labourer, P.StMary
5, 1, 4, CAIN, Robert, Laghan, Son, Unmarried, 17, Ships Carpenter, P.StMary
5, 1, 4, CAIN, Thomas, Laghan, Grandson, , 14, Scholar, Malew

"Our" Ann was clearly born in 1848
1851 Rushen
John Caine 25 ag lab b Malew
Ann 29 Rushen
Betsey 4
Ann 2
Cath 1

Perhaps someone could check the Rushen baptism records to see if/how she is listed.

Will need to flesh out info on Wm Caine/Elinor Mylechreest
Wm Caine md 20 July 1782 Santon to Elinor Mylchreest
1. Thomas 26 Oct 1783 all Marown
2. CHARLES 11 May 1794
3. Samuel 1 Jan 1785
4. Elilnor 17 Sep 1786
5. Robert 2 Aug 1789
6. Samuel 26 Apr 1791
7. Ann 4 Oct 1795
8. Elinor 18 Jun 1797
9. Margaret 18 Jun 1797
10. James 10 Mar 1799

Genealogy "takes a village"

Donna