Greg, I think I have found brother John still in the Isle of Man.

Maughold marriage:
30 Apr 1870
John CORKILL Full age Bachelor Blacksmith Maughold [father] Robert Corkill, Blacksmith, and
Margaret WATTERSON Full age Spinster Maughold [father] Robert Watterson, Miller.

He wasn't found there in the 1871 census, but is there in 1881:
John CORKILL Head M Male 31 Isle of Man, Blacksmith
Margaret CORKILL Wife M Female 32 Isle of Man
Harriet M. CORKILL Daur U Female 12 Isle of Man, Scholar
John R. CORKILL Son U Male 10 Isle of Man, Scholar
Frederic CORKILL Son U Male 8 Isle of Man, Scholar
William CORKILL Son U Male 6 Isle of Man, Scholar
Thomas A. CORKILL Son U Male 4 Isle of Man, Scholar
Ann J. CORKILL Daur U Female 8 months Isle of Man, Scholar
Source Information: Dwelling 10 Queen Street, Maughold, Isle of Man
Family History Library Film 1342346
Public Records Office Reference RG11
Piece / Folio 5601 / 7 Page Number 13
[from FamilySearch]

Youngest daughter Ann Jane is on Brian Lawson's list of registered births as born 1 Aug 1880 Ramsey daughter of John CORKILL and Margaret WATERSON.

Sue