Hi Paul,
The 1911 census info which I posted for Thomas & Isabella and family fitted some of the details which you gave from the marriage. Married about the right length of time, IOM given as Thomas's birthplace, and Rosshire for Isabella's. Also Isabella's age was not far out bearing in mind that people were inclined to take a couple of years off their ages as they got older.

I've just checked IOM registered births (compiled by Brian Lawson), seeing that some of their children in the 1911 census were born there, and guess what!
William KELLY, [born] 19 Aug 1888, [registered] Mic[hael], [father] Thomas KELLY, [mother] Isabella MC DONALD.
(Eldest son given in 1911 census.)

Thomas Henry Mc[Donald?] KELLY 19 Jan 1892 Mic Thomas KELLY Isabella MC DONALD
(To fit in the columns Brian cut off the last part of forenames if too wide.)

Isabella Alice KELLY 23 May 1890 Mic Thomas KELLY Isabella MC DONALD
(Died young?)

Isabella Alice KELLY 27 Jul 1896 Pee Thomas KELLY Isabella MAC DONALD
("Alice" in the 1911 census.)

Margaret Willin[a] KELLY 16 Nov 1898 Mic Thomas KELLY Isabella MAC DONALD
("Willena" in census.)

Isabella could have had Annie the year after the census - it wasn't unusual to have a baby at that age, sometimes called a "menopause baby" (which is a misnomer), especially after having had a number of earlier children.

Sue