Well done, Lois. That's a lot of good detective work. This has filled in some gaps for me too.
I think the answer to why Isabella Killip als Quay isn't mentioned in the 1740 will of Catherine Kermott is that she died in 1738. Her husband Patrick was buried 6 days before her, both in April 1738 at Lonan. Their wills (separate) only list their children.
I think William KERMOD is the son of Daniel KERMOD & Ann FARGHER. Daniel died in Jan 1724/5 and Ann in 1699. I see wills on the index for both and apparently I had seen Daniel's will sometime in my past because I have a note it mentions "dau Catrin" These will be on Frances's site, which isn't handy to me at the moment.
Catherine Kermott's 1740/41 will mentions "William Kermott her brother's son" and "James Kermott her brother". I think James will match the marriage 17 Nov 1718 Lonan to Joney CLAGUE. They are my 6xg-grandparents, via their daughter Jane b 1722. Jane married Patrick Killip, the son of Patrick Killip and Isabel Quay. I think we recognize those two!