Have you looked at this website?
ww.iomfhs.im (go to research)
Births/marriages/Burial details courtesy of Brian Lawson.
From there I have found these details

Marriages of siblings:-
DAUGHERTY, Selina Margaret 3 Sep 1899 D dsg 216a SAYLE, William George
Births on the site go to 1901 and found one child born to the couple to that date:-
SAYLE, Elsie Gertrude 17 Jan 1900 Dou SAYLE, William George DAUGHERTY, Selina Margaret

DAUGHERTY, Stanley 24 May 1896 D dsg 123b KILLEY, Louisa
three children found
DAUGHERTY, Medina Anni 27 Feb 1897 Dou 1282 DAUGHERTY, Stanley KILLEY, Elizabeth Louisa
DAUGHERTY, Robert John 7 May 1900 Dou 1508 DAUGHERTY, Stanley KILLEY, Elizabeth Louisa
DAUGHERTY, Stanley Her 5 Jul 1898 Dou 1376 DAUGHERTY, Stanley KILLEY, Elizabeth Louisa

DAUGHERTY, Elsie Gertrude 12 Nov 1911 D dsg 436a QUIRK, John Allen

Looks like there was also a sibling John A (aged 2 1881 Census) this could be him
DOUGHERTY, John Alvea 8 Sep 1897 D RC 102 COWLEY, Catherine Jane

However you said your Grandfather was John William - two Johns? There are births registered to this couple (he is down as John Alma on births of children) and this could be his burial though age out a couple of years
DAUGERTY, John Alma 70 Bra 23 Dec 1946

Burial Register:-
DAUGERTY, Medina Annie 17 Bra 24 Jan 1893
Looks like Medina also had a daughter just before she died so possibly died in childbirth?)
DAUGHERTY, Medina Anni 21 Jan 1893 Dou 1007 Not given DAUGHERTY, Medina Annie (d

Also in Burials
SAYLE, Selina Margaret 83 Bra 5 Jun 1960
QUIRK, Elsie Gertrude 67 Bra 2 Feb 1955 DAUGHERTY, Harold 39 Dbc 2 Feb 1930

Possibly someone with access to 1901 census could help you further.

Hope this helps a little

Sandra