Kelly, I have Cronin, McCarthy and Sweeney in my ancestry. My ggf parents are supposed to be Denis McCarthy and Mary Cronin... or Hannah Cronnen/Crounen. They went to Wales where their children Denis, Patrick, Hannah, Ellen and Mary Ann were born from 1859 to 1865. They emigrated to Pittsburgh in about 1872. The only Wales census with a Denis Jr of the right age is 1861 and gives parents as Jeremiah (spelled Jerynnah) and Mary.
There's an 1854 marriage of Denis McCarthy and Mary Cournane in Tralee; witnesses Timothy Collins and Jeremiah Cournane. Otherwise I can find no marriage for them in the records on irishgenealogy.ie.
My Sweeney is Margaret Sweeney, b. 1812 who married Timothy Carroll. They had daughters Mary and Johanna who married brothers Daniel and Denis O'Leary. Daniel is my gggf. The O'Learys are my father's mother's family; the McCarthys are my father's father's family. All ended up in Pittsburgh. The O'Learys settled in Wheeling, WVA, but my ggf and a couple of his brothers went to Pittsburgh.
Are you on ancestry? Look me up-- I'm MegMS; my tree is called Callahan Family Tree.