The MI for John Wilfred Cowin b 1896 who was killed in 1917 in WW1 has clarified things. There are 2 possibilities for the JWC who married Evelina Christian Robinson.
1) a JWC whose birth isn't in the index of Manx births --- perhaps born on the mainland.
2) JWC b 1893 son of Thomas Benjamin Cowin and Elizabeth Jane Christian. Here is his family in Douglas:
1891
Conchan 6/15
16 Bigwell St
Thomas Cowin head mar 26 carter b Santon
Elizabeth wife 21 b Douglas
William son 3 b Douglas
Thomas son 2 b Douglas
Florence dau 5 months b Douglas
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1901
5305 95 208
Conchan 5b/26
Hardys Cottage, Shaw's Brow
Thomas Cowin head mar 38 carter
Elizabeth wife 33
William son 13
Thomas son 12
Florence dau 10
John son 7
Robert son 5
Elizabeth dau 3
Catherine dau 1
all b Douglas, except Thos sr b Santon
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Marriage of John Wilfred Cowin b 1893's parents:
COWIN, Thomas 24 Nov 1888 D bra 301b CHRISTIAN, Elizabeth
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This might be the William age 3 in 1891 and age 13 in 1901:
CHRISTIAN, William Ben 30 Jan 1888 Douglas 687 Not given CHRISTIAN, Elizabeth
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These are the children born after their parents' marriage:
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COWIN, Thomas Herbert 25 Feb 1889 Douglas 760 COWIN, Thomas Benjamin CHRISTIAN, Elizabeth
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COWIN, Florence Annie 23 Oct 1890 Douglas 866 COWIN, Thomas Benjamin CHRISTIAN, Elizabeth Jane
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COWIN, John Wilfrid 10 Apr 1893 Douglas 1021 COWIN, Thomas Benjamin CHRISTIAN, Elizabeth Jane
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COWIN, James Robert 3 Jul 1895 Douglas 1170 COWIN, Thomas Benjamin CHRISTIAN, Elizabeth Jane
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COWIN, Elizabeth Ellen 4 Apr 1898 Douglas 1361 COWIN, Thomas Benjamin CHRISTIAN, Elizabeth Jane
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COWIN, Catherine Jane 26 Jun 1899 Douglas 1447 COWIN, Thomas Benjamin CHRISTIAN, Elizabeth Jane
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There's a marriage of a John Wilfred Cowin at St George's Douglas in 1919, index no 566 311.
If you send for the certificate, you'll find out whether this is the JWC who married Evelina, and you'll find out the names and occupations of their fathers, to confirm that the family above is the right one (or not).
Jean C