Jeff, this is all very useful. Reading the passage from the Radcliffes' A History of Kirk Maughold, pp.280/1, one might suppose that each John was the son of the previous one, but you have found that the third John was the son of Daniel, brother of the second John.
You have clearly studied these Kerruishes in the Maughold registers. Is Kerruish your specialism? If so, I would be interested to know if you have been able to sort out the family/ies at Baldromma Beg. Are you descended from Glen Vullin?
There is just one query. You have the first John Kerruish, husband of Margaret Corteen, born in Glen Vullin. In the Radcliffes' book they say that this John married in 1670 Margaret Corteen, heiress of the land, which suggests that it was Margaret, rather than John, who was born at Glen Vullin. Are these birth and death places surmises on the principle of continuity?
If you would like to write to me by e-mail, I am at firstname.lastname@example.org.