Great, thank you. You gave the PRONI reference for the collection, but I dumbly assumed that to browse in it I would need to visit PRONI, which isn't going to happen.
So it's established that Bristow Johnson is a brother of Henry, a nephew of Alexander Mackey, and a son of Mary born Mackey. And it's plausible that the reason why Bristow Johnson is a witness at the marriage of Mary McLorinan is that he is her cousin; she is a daughter of Mary's sister Martha, who became the mother of the Rev. Thomas McLorinan. And it's plausible, from the Simpson connection, that the spinster Martha McLorinan is another daughter of Martha Mackey, another sister of the Rev. Thomas McLorinan.
I think John McDowell's wife Elizabeth is another daughter, a sister of Mary, Martha, and the Rev. Thomas. That her maiden name is McLorinan is near enough certain. As Shanreagh noted, two of her children have McLorinan as middle name. (Jane is Jane McL. McLorinan on John's gravestone, but what else is that if not McLorinan? Henry is definitely Henry McLorinan McD.) An extra bit of evidence: her son John junior calls his first daughter Elizabeth McLorinan McDowell, surely in honour of his mother. (She is Elizabeth McClernon McD on the civil record of her birth [Larne, June 21 1886], but on his will probate she is Elizabeth McLorinan Napier, married woman, daughter.)
The only problem is the profession of the person who is coming into view as Martha McLorinan's husband Henry McLorinan, the father of these siblings: Rev. Thomas, Mary, Martha, and Elizabeth. The Henry McLorinan who died in the presence of John McDowell in 1875 is a farmer. The father of Martha is a shopkeeper. In between, the father of Mary is a farmer? or perhaps grocer? And we know there is a Henry McLorinan grocer, and sometimes haberdasher, in Antrim at the time. The only suitable Henry McLorinan on the civil records of deaths in Antrim around the right time is the one who died in 1875. So I'm stuck with my question: could he have been both a farmer and a shopkeeper, specifically a grocer/haberdasher?