Hello Lynne. Good observations about the Margaret Gelling als Kneale vs Christian problem.
I had looked at these folks as part of my on-going GELLING research project. This particular John Gelling of Camlork caused me some grief, but after a while I determined he married 3 times. Wife #1 and wife #3 had the same name, Margaret Christian.
John Gelling was probably born ca 1634 s/o Paul Gelling Jnr & Isabella Lewin. John was the eldest and therefore heir of Camlork. He married first wife Margaret Christian ca 1655 and they had a daughter perhaps named Margaret. Wife Margaret buried 17 Apr 1657. Her father Ewan Christian left a 1663 Maughold will that mentions "due to John Gellin's daughter from her Grandfatherxxxx 7 pounds which doth appear in her mothers inventory and bonds. His will is here: familysearch.org/ark:/61903/3:1:3Q9M-CSND-YBFC?i=353&cat=233934 [354 of 523 + before + after]
My suggestion is that John Gelling next married Catharine Kelly ca 1660 and they had a child Jane in 1661, and possibly children Joney, Robert & Mary before she died in 1674. Son Robert was buried the day after her and all 4 children died early.
In 1663 John Gelling's father Paul Gelling died and left a will that mentions a grandchild Jaine 1 sheep & lamb and grandchild Margrett Gelling 1 sheep & lamb, who I think must be children of John because Paul's other children are likely unmarried.
About 1675 John Gelling married wife #3 also named Margaret Christian. She died 1724/25 and John likely died before her, though haven't determined a date yet. They had children Paul (1676-1736, heir), John (ca 1680-1738 of KK Michael), and Elizabeth (1685-1753 md John Kewley).
You are right that the surname "Kneale" appears in the MNB extract, but doesn't appear anywhere in the transcribed will. It turns out there is another John Gelling & Margaret als Kneale living at the same time in Douglas. He died shortly before the above Margaret, in Nov 1724 and his will mentions wife Margret Gelling alias Kneal, plus children who clearly are a different family. Margaret Gelling als Kneal of Douglas Widow left a 1735 Braddan will, and the children match well.
The document "Kewleys of Ballafreer" in the IOMFHS Journal July 1985 and also in the MNB states that Elizabeth Gelling's mother was the daughter of William Christian of Balnekilley KK Maughold.
I've never looked to see if the two Margaret Christian's are related in some manner. Each were from Maughold, but different fathers Ewan and William.
Looking back over all of this, there's a good deal of conjecture here. It presumes the name "Kneale" as alias for the latter Margaret is incorrect and it should be Christian. It assumes the William Christian as father as noted in the above named document is correct. It presumes there's a middle marriage for John Gelling. I liked it because it meant everything else fitted well together, and no other possibilities did. But it could be wrong. I'm open to ideas.
I hope I haven't confused matters too much.