Hello Peter. I've only recently looked at all these Kewleys in any detail, so I think I'm way behind you. I'm not surprised that I didn't add anything useful for you but if we're on the same wavelength and I didn't say anything contradictory to your research, I'm encouraged.

Re the 1719 baptism Lonan baptism, if it were this Gilbert Kewley he'd be only 17. I just looked at the image of the Lonan baptism and it is interesting: "Mary Carran Daught'r to Gilbert and Margt Kewley alias Carran was bapt 2'd Aug't 1719". I we switch the surnames after "Margt", it would be "Carran alias Kewley", and thus it would be Gilbert Carran. Switching the alias's was quite common in the 1600s, and perhaps in the early 1700s too? Also, the "rr" in the middle of "Carran" is almost an "n", which could make it "Canan". So, there's some doubt in the interpretation. But if it really is Gilbert Kewley, it could be connected to one of the Lonan Kewleys in some way.

Re the rest of your note, I agree. Too much not yet known. I stabbed a bit at the Corletts and quickly felt a headache coming on. I have uncertainty with every one of Gilbert and Joney's six children too.
Could #1 Esther b 1726 be the one who married Henry Faulkener of the Royal Navy 1771 Braddan? She's mentioned as a sib in brother John's 1757, but not in either parent's 1771 & 1779.
#2 John b 1727 left a 1757 will that mentions sibs Robt Thos Esther & Mary, and a wife but who is the wife?
[perhaps] #3 Richard buried 1735 s/o Gilbt K but no bapt.
#4 Mary was wife of James Corrin; are they the couple married 22 Nov 1748 Lonan? Why is she "dau Jane" in father's 1771 will? Their eldest Jane Corrin (bapt date?) md Thomas Quine 1774 Braddan, but why is she called "niece jane quine als Corrin" [instead of g-daur] in grandmother Joney's 1779?
#5 Robert b 1731 I've placed to have md Ann Clark 1760, but can't prove it.
#6 Gilbert b 1734 disappears. But a brother "thos" appears in #2 John's 1757 extract, but I don't see anywhere else.

Always some mysteries.
Eric