Hi - I agree with almost everything you have written. My only reservation is if an elder son was alive they would usually mention in the deed why he was not inheriting the property as eldest son and heir, just as they did in the 1769 deed. Being "beyond seas" is given in many wills. - But it is an interesting thought, and worth looking at.

I found these Maughold parish register entries for Ann Cannell:
John Looney / Ann Cannell married 9 Aug 1795. Ann had guardian's consent.
Possibly: Anne daur of Robert Cannel/Mary Callow bapt 26 Jul 1775.

Ann LOONEY als CANNELL buried Jul 28 1797.

I didn't find any bapts for their children.

When I was looking at the Maughold register transcripts I looked again at the dates of the children who John Looney and Margaret Kelvie had baptised, because of the argument that son John who was buried 2 Dec 1835 aged 87 could not have been born c.1748 because Thomas was bapt 14 Aug 1748.
Apparently they had forgotten to have William or John baptised.

It occurred to me that if John was born, say, Nov.1747, that still makes him aged 87 at death in Dec.1835 (not that the exact year matters).
In the 1832 deed where he transferred his land to his eldest son John he wrote “ I the said John Looney being now aged and infirm and unable properly to attend to my own affairs…”

One thing I forgot to mention before was that not only was the 1769 agreement signed by all parties including by father John Looney, but the addendum after his death had “And whereas Margt, (the Widow of the Testator) now wife of Wm. Creetch with her said present Husband have in Court consented & agreed to this Will in every Respect & that Daniel Looney & John Looney have also acknowledged & consented thereto…”

Sue