Hello Pauline,
About needing consent to marry underage, I've checked Tom Corteen's transcript of the original Maughold register. As you wrote previously this consent was not included on the marriage record of Robert Calcoat & Joney Garrett on 22 May 1744. However Tom transcribed the entries as written and in date order as they appeared in the register volumes, and it looks as though the vicar only started to add the record of the "consent" of parents/guardian after 1760. This was the first entry:
Rich Ambrose Stevenson & Marjery Frissel 24 Mar 1761. Richard (Esq) of Malew, Marjery Maughold. Both with consent.
After this there were many entries with the consent included. So your couple could well have had consent which wasn't recorded in the register.
I can't see a Maughold burial for Margaret Garrett als Kelly in the time-frame (William's first marriage 1739; second marriage 1751). Or were these different William Garretts?
Before posting this I checked the board and see that Averil found Margaret Garrett als Kelly's burial in 1756! (Assume Lezayre?) But didn't William Garrett and Isabel Fargher have children before then, and married in 1751? Could his two marriages have been the other way around? Or not the same William Garrett. It might be easier if you write a separate message on the board for each couple, because having so many together is very hard to follow unless you know the families?
Sue