Hello Wayne,

The Maughold parish register has George William son of William Kelly & Elizabeth Gelling bapt 11 Apr 1841 by Revd W Christian at the Dhoin.

I had a look at the 1851 census which you mention, to double-check the second William aged 7, and he was b.Braddan. I think it is unlikely that George Wm would be known as William when he had a living brother with that name?

Daughter Elizabeth aged 3 is on the IGI (extracted record) bapt 6 Feb.1848 Lonan with mother Elizabeth Helling, rather than Gelling. She was also Helling for James Henry's bapt Lonan in 1854. In the 1851 census she was b.England, and son John 13 was b."Conestione" Eng.
There is a marriage for WILLIAM KELLY & ELIZABETH HELLING 9 JAN 1837 Hawkshead, Lancashire.

The IGI [Familysearch.org] has an extracted entry for the marriage of GEORGE WILLIAM KELLY to MARY MARTHA TRELOAR (not Kelly) on 22 FEB 1868 Lonan. She is recorded in the 1871 census as b.Wales.

What makes you think George died and she remarried, rather than, for example, the family went to England or Wales? Have you found Mary Martha in a later census?

Sue