Hi - How old was Isabella McDonald in 1887? Did you find the couple in the 1891, 1901, and 1911 censuses? If so please post their addresses, ages, and places of birth in each/any one of those?

The only Thomas Kelly son of William, bapt in Michael that I can find around the age given at his marriage, appears to have stayed in the IOM and married Jane.
Which document gave your Thomas Kelly's mother's name as Elizabeth?

In 1911 there is a Thomas Kelly, aged 49, a married fisherman and master of the "Vessel: Village Belle No 162; Port/place: Glenmay Patrick Isle Of Man". His birthplace is also given as Glenmay Patrick I O Man.

There is also this family:
Name Relation Condition/Yrs married S ex Age Birth-Year Occupation Where Born:
KELLY, Thomas Head Married M 52 1859 Stationary Boiler Stoker Kirk Michaels I O M Resident
KELLY, Isabella Wife Married 23 years F 44 1867 Rosshire Scotland
KELLY, William Son Single M 22 1889 Locomotive Machine Man Kirk Michael Isle of Man
KELLY, Henry Son Single M 19 1892 Apprentice Locomotive Blacksmith Kirk Michael Isle of Man
KELLY, Alice Daughter F 14 1897 Housemaid Domestic Peel Isle of Man
KELLY, Willena Daughter F 12 1899 School Kirk Michael Isle of Man
KELLY, John Son M 6 1905 Earlestown England
KELLY, Stanley Son M 4 1907 Earlestown England
RG number:RG14 Piece:23116 Reference:
RG14PN23116 RG78PN1350 RD459 SD1 ED15 SN219
Registration District:Warrington Sub District:
Newton in Makerfield Enumeration District:15 Parish:Newton in Makerfield
Address:
346 Wargrave Road Newton Le Willows Lancashire County:Lancashire

Sue