The more wills, the better. My favourites are those that say something like "I give to the wife of my brother John Gelling, namely Isabella Cavendish, a hog and an apron to use as she wishes". We may not find that, but hopefully something will show up. Of course, not everybody had a will particularly if they had no assets to distribute.

I copied a number of Gelling burials off a film the Braddan register about 20 years ago. These entries are relevant to this discussion:

Braddan Burials (a mix of old and new Church, which I didn't differentiate unfortunately):

Margt Gelling als Quilliam (Ballamillaghyn) May 12 1822 [no age given].
John Gelling (Ballamillaghan) age 89 Jul 31 1829.
John Gelling Ballamillaghan bur Feb 23 1854 90 years died at the Ballaghe KK German.
Elizabeth Gelling Ballagh KK German late of Ballamallaghyn Jul 13 1855 88.

Subtract 90 years from 1854 and you get 1764, the exact year of the baptism of John G at Marown, son of John G and Margaret Quilliam. The 1851 census has them (John G & Elizabeth) at KK German and he is stated as being born at Marown. This all matches perfectly. I have not seen the wills, though.

John Gelling & Elizabeth Oates married at Braddan in 1787 and they had 7 boys and a girl Elizabeth, starting with a John of course (to keep up the long-standing tradition). The first 5 boys all were buried at Braddan 1819-1827 and have Ballamillaghan and the correct ages. Number 6 boy Robert married and had children but he died before his parents too. That left the youngest Philip b 1810, 6 years after Robert. Philip is heading Ballamillaghin in all the census's from 1841 to 1881. I haven't tried to find Elizabeth bp 1799 yet.

I only wish all the other Gellings were as clearly identified as the Ballamillaghyn group is. Try as hard as I can, I can't see how John Gelling / Isabella Cavendish fits into this group, but where he does fit remains a mystery to be solved.