I don't have your chaps listed in my collected genealogical trees which are mostly taken from Burkes Landed Gentry and Commoners, but the Ormsbys of co Mayo were mostly descended from Malby ancestor of Ormsby of Cloghans Co.Mayo who married Ross O'NAUGHTEN. Though they did marry Ormsby cousins from Sligo and elsewhere.
Malby & Ross had a son John who married Winifred JORDAN. They had a son, Robert of Cloghans d.1700/14 who married Mary BLAKENEY and had 7 sons. Their 6th son, Oliver married Deborah (dau of Col. BARRY). Their son John (1752) of Pittsburgh, Pa., married in 1764 Jane b.1747 (of Archibald McALLISTER) and had children: John, Oliver who married Sarah MAHON,Jane who m. Dr Nathaniel BEDFORD, Joseph, Sidney who m. Isaac GREGG.
Places mentioned in Burkes in association with Ormsby in co Mayo are Foxford, Cloghans, Gortner Abbey, Killiney, Crossmolina, Ballinamore, Knockmore.