You have posted your message in a parish in Co. Armagh, whereas your ancestors appear to come from the civil parish of Kilkeedy in Co. Clare (Killkeady RC parish) which is about 250 miles away, at the other end of Ireland. You might want to post your message again on the Kilkeedy parish board, as that way people with knowledge of the area are more likely to see it.
The spelling of your family’s surname varies from record to record. That's very common. It doesn’t indicate a deliberate change of name just that the spelling was down to the whim of the person recording it. Many people those days couldn’t read very well, but in any event having a “correct” spelling of your surname wasn’t something they bothered about. Don’t rely too heavily on any age or date of birth you may have found in US records. Most people in Ireland in the 1800s didn’t celebrate birthdays and often had little idea of exactly when they were born. If officialdom asked them their age or date of birth, they often just guessed or made one up.
In the tithe applotment records for 1842, there were 4 Geegan/Gegan households farming in Poulataggle: Patt, John, James & Joseph.
In Griffiths Valuation for 1855, there were 3 Geoghegan households in Poulataggle. John junior, John senior and Michael. Together with 2 other farmers, they farmed 465 acres of land. Patt, James & Joseph don’t appear in the 1855 records so the chances are they have either died or emigrated. Some of their descendants will likely have acquired their farms.
By the 1901 census there were 6 houses in the townland, and again 3 occupied by Gegan/Geagan families:
By 1911 there were still 6 houses, 2 of which were occupied by Geoghegan families and 1 by a Geagan:
Statutory birth registration only began in Ireland in 1864. Prior to that you have to rely on church records. The records for the RC parish of Killkeady start in 1833. The RC parish records are on-line free on the National Library site:
You might want to search them for Bartholomew and any siblings. (I can see Pat Gegan born to James Gegan & Ann Carney in 1844. You can easily scroll through looking for others.)