Hi Jean & Averil,
As Averil's dates have him born between 1862 and 1868 I looked for 5 years either side of 1865 (before posting that previous message). That's why some bapts were as late as 1870, which is probably wrong, but the only John Henrys found in Braddan.

These were the possibles I found in the 1871 census (household index), if you can see anything there to investigate further (and hoping that Robert might have been John Robert! - grasping at straws).

Name, Relation, Condition, Se x, Age, BirthYear, Where Born
CAIN, Jonathan Head M 54 1817 Isle of Man
CAIN, Jane Wife F 48 1823 Isle of Man
CAIN, Emily Daughter F 16 1855 Isle of Man
CAIN, Ann M Daughter F 14 1857 Isle of Man
CAIN, John H Son M 9 1862 Isle of Man
CAIN, Margt E Daughter F 8 1863 Isle of Man
CAIN, Eliza J Daughter F 4 1867 Isle of Man
RG number:RG10 Piece:5775 Folio:84 Page:22
Civil Parish:Conchan Address:Albert Street, Conchan, Douglas County:Isle of Man

CAIN, Robt Head M 42 1829 Isle of Man
CAIN, Margt Wife F 43 1828 Isle of Man
CAIN, Robt Son M 18 1853 Isle of Man
CAIN, Thos Son M 14 1857 Isle of Man
CAIN, John Son M 11 1860 Isle of Man
CAIN, Joseph Son M 8 1863 Isle of Man
CAIN, Philip Son M 4 1867 Isle of Man
CAIN, Christian Daughter F 1 1870 Isle of Man
RG number:RG10 Piece:5771 Folio:64 Page:8
Civil Parish:Patrick Address:Ballahigg, Patrick County:Isle of Man

DUKE, William Head M 62 1809 Isle of Man
DUKE, Jane Wife F 64 1807 Isle of Man
DUKE, Lisa Daughter F 20 1851 Isle of Man
CAIN, John Boarder M 10 1861 Isle of Man
RG number:RG10 Piece:5776 Folio:149 Page:25
Enumeration District:6 Civil Parish:Douglas
Address:Quay, South, Douglas County:Isle of Man

CAIN, John Head M 36 1835 Isle of Man
CAIN, Catherine Wife F 37 1834 Isle of Man
CAIN, John Son M 2 1869 Isle of Man
CAIN, Thomas Edward Son M 0 1871 Isle of Man
CORKHILL, Esther Sister-In-Law F 21 1850 Isle of Man
RG number:RG10 Piece:5777 Folio:43 Page:14
Enumeration District:3 Civil Parish:Braddan
Address:Cronkbourne 5th, Braddan County:Isle of Man

CAIN, John Head M 36 1835 Isle of Man
CAIN, Margaret Wife F 35 1836 Isle of Man
CAIN, John Thomas Son M 11 1860 Isle of Man
CAIN, Elizabeth M A Daughter F 9 1862 Isle of Man
CAIN, Jane Daughter F 7 1864 Isle of Man
CAIN, Gertrude C Daughter F 4 1867 Isle of Man
CAIN, Henery Son M 1 1870 Isle of Man
RG number:RG10 Piece:5771 Folio:83 Page:2
Enumeration District:1 Civil Parish:German
Address:Balla Kaighen, German County:Isle of Man

CAIN, John Head M 45 1826 Isle of Man
CAIN, William Son M 19 1852 Isle of Man
CAIN, Eleanor Jane Daughter F 14 1857 Isle of Man
CAIN, George Son M 12 1859 Isle of Man
CAIN, Louis Son M 9 1862 Isle of Man
CAIN, Henry Son M 5 1866 Isle of Man
RG number:RG10 Piece:5776 Folio:46 Page:27
Enumeration District:2 Civil Parish:Conchan
Address:Bigwell Street, Conchan, Douglas County:Isle of Man

Sue