John Edward Cretney married Elizabeth Gelling 30 Nov 1905 in Santon, and as of the 1911 census they had 3 children.

1911 census at 23 Allan St, Douglas RG14/34665 RD635 SD3 ED18/12 SN77 (3 rooms)
John Edward CRETNEY, Head 27 Married, Van Driver, Baker, Worker, b Isle of Man Santon
Elizabeth CRETNEY, Wife 27 Married 6 yrs, 3 born 3 living, b Isle of Man Santon
Elizabeth Mildred CRETNEY, Daughter 4, b Isle of Man Santon
Richard Arthur CRETNEY, Son 2, b Isle of Man Douglas
Elsie May CRETNEY, Month??, b Isle of Man Douglas

Elizabeth's younger sister Mildred Gelling married Robert Edward Faragher 11 Jul 1907 Santon, and as of 1911 they had 2 children.

1911 census at Santon Villa, Santon RG14/34749 RD635 SD2 ED8/1 SN41 (4 rooms)
Robert Edward FARAGHER, Head 24 Married, Platelayer Railway, Worker, b Isle of Man Malew
Mildred FARAGHER, Wife 22 Married 4 yrs 2 born 2 living, Gatekeeper Railway, b Isle of Man Malew
Robert Gelling FARAGHER, Son 3, b Isle of Man Santon
Richard James FARAGHER, Son 1, b Isle of Man Santon

These match the Faraghers (from Brian Lawson's burial index):
Burial: FARAGHER, Robert Edward 78 San 20 Jun 1965
Burial: FARAGHER, Mildred 82 San 23 Dec 1871 [typo? s/b "1971"?]
Burial: FARAGHER, Robert Gelling 71 San 24 Jul 1979
Burial: FARAGHER, Richard James 19 Santon

None of the Cretneys appear on the IOM Burial list, nor in FreeBMD. Perhaps they emigrated?