Have you by any chance done DNA testing? I strongly believe my McCarthys- mostly found in Lixnaw village- were from the Kilfeighny group. My earliest confirmed ancestor is Patrick McCarthy who married Ellen Collins and lived in the village and briefly in Irrebeg between 1832 and 1840, the time which his known baptized children were born. I can't identify his own baptism record with any confidence, but I did notice that there was a Florence McCarthy, the name he gave his own 3rd son, who was about the age Patrick would be expected to be (born Kilfeighny 1812). That Florence was the son of a Denis McCarthy (probably born about the 1780s), which is the same name my Patrick gave his eldest son. I suspect my Patrick and 1812 Kilfeighny Florence may have been brothers, with Patrick being perhaps a few years older and therefore not represented in the baptism records, which seem to begin around 1810. The only name you mentioned on your post that isn't familiar among my known family is William, but if memory serves, 1812 Florence did name a son William, along with Denis. It wouldn't shock me to learn that you are descended from this Florence, though there were several other appparently related McCarthy men in Kilfeighny (though Florence ended up in Tullig nearby).
I'd love to explore the possibility that we are related in a way that can be ascertained. Please contact me to discuss this. Also, if it helps anyone at any point, my McCarthys carry a I-L1498 Y chromosome.
I might also suggest looking up Nora Kissane, a local genealogist whose husband comes from the Kilfeighny McCarthys, including one named William, if memory serves.