Sorry, but I reckon your church didn’t exist in 1790.
From Ros Davies freepages.genealogy.rootsweb.com/~rosdavies/PLACENAMES/BanBy.htm#Bo
Boardmills {civil parish of} Killaney 20: 35/60 small village in Carrickmaddyroe townland ; half way between Saintfield & Lisburn; click here to see its location on a map; there was a Reading Scoiety here in 1830; school: 2 Presbyterian churches here; Temperance fete 17 Jul 1886 V12 p101 OSM; SHM ;86 p 45; DR; GIPR
Ros says under her Churches section
2nd Presbyterian Church, Boardmills at the western end of the street. The congregation separated from First Boardmills Presbyterian in 1809
Records available are baptisms 1836- 1866, try
www.familysearch.org Batch #C700091; graveyard attached, gravestone inscriptions UHF Vol 2; The oldest stone in the graveyard dates from 1821 ; email me for a gravestone look-up or pay per view gravestone inscriptons on
www.irishgenealogy.ieSurely you need First Boardmills Presbyterian records about which she says
Baptisms 1782- 1889, marriages 1782- 1844 & 1851-1870, try
www.familysearch.org Batch # C700011; graveyard nearby, gravestone inscriptions UHF Vol 2;oldest date of death on a headstone is 1778; email me for a gravestone look-up or pay per view gravestone inscriptons on
www.irishgenealogy.ieSwitching to Ros surname listings, she doesn’t have McFarl…. In Killaney parish and she has one martin mention.
Miss Mary MARTIN . Killaney wife of William Kidd ; mother of Sarah b. 3 Jan 1854 & twins, Agnes & David b. 19 Oct 1855 & Thomas Hall Kidd b. 11 Nov 1857 & Elenor b. 22 Aug 1860 (all bapt. Boardmills Presbyterian Church) PR
I had a look at PRONI leaseholders and Griffiths valuation heads of households about1860 but didnt see either surname in the parish. Familysearch seems the most promising source, but i reckon you have been there. Good luck onwards, Jim