Not sure if this is helpful or related, but I've been capturing baptism sponsors & marriage witnesses into a spreadsheet of my ancestors, and there is a Mathias Myers listed as a sponsor at the 10 Jun 1829 baptism of Richard Coughlan in Cullina - which is not too far from Kilclooney. I'm thinking that Mathias would be a potential sibling to your John. Just had to throw it out there in case; the other names that appear on the record are parents Thomas Coughlan & Honora Duane, and my ancestor, Catherine Keys.
Good luck in your search, and if you happen upon the names of any of the others, please reach out!
Mary Anne
KeyesMcNicholas1845!