I just looked at the thread that Chempat gave a link to and see that it mentions John being a solicitor.
That being the case I found him on the 1911 with parents Thomas and Annie and two younger sisters.
Birthplace Newcastle on Tyne.
1911c
https://www.familysearch.org/ark:/61903/1:1:XWMW-MJ6John is not with his family on 1901 census
https://www.familysearch.org/ark:/61903/1:1:XS9S-FRFThis could be him
John ISMAY Age:16, Pupil
Birth Place: Newcastle Upon Tyne
Town: Bedford
Piece: 1493
Folio: 43
Page Number: 35
EDIT John ISMAY mmn
LOWNDS 1884 D Quarter in NEWCASTLE ON TYNE Volume 10B Page 143
there are these details on family search
Ernest Ismay 1922 marriage British Columbia
https://www.familysearch.org/ark:/61903/1:1:JDZ1-9F2Eileen Ismay
29 Sep 1891 Jesmond, Northumberland, England, United Kingdom
Father's Name:
Thomas Parker IsmayMother's Name: Annie Julloch
Mabel Ismay
09 Oct 1896 Jesmond, Northumberland, England, United Kingdom
Father's Name: Thomas Parker Ismay
Mother's Name: Annie Pullock
Thomas Parker Ismay Age: 24 single, father John
Spouse
Annie Tulloch Lownds Or Lounds 21 father James Richard Lownds or Lounds
15 Jan 1881 Newcastle-Upon-Tyne, Northumberland, England
Thomas Parker ISMAY of 1 Dilston Terrace Gosforth Northumberland and of The Northern Conservative & Unionist Club died 28 Nov 1930
Probate to
John Ismay company Director
Herbert Arthur Ismay age 76
Event Date: 25 Mar 1960 Duncan, British Columbia, Canada
Marital Status: Widowed
Birth Date: 04 Jun 1883 Newcastle, England
Spouse's Name: Barbara Stuart
Father's Name:
Thomas Parker IsmayMother's Name:
Annie Tullock LowndsGRO indexes has mmn LOWNDS/LOUNDS for
Herbert Arthur, Ernest, Olive Winifred, Eileen, Mabel ISMAY