Looking for O'Gallagher ancestors

My husband and I are coimng to Ireland from the USA for the first time in October for 3 weeks. I believe I have traced my 3rd great grandfather, 4th great, and fifth great to Donegal. This is what I know. 5thgreat grandfather named John Thomas O'Gallaher. Born inKillaghtee Parish in 1716. Died in 1798 inBallyshannon, Donegal. My 4th great grandfather was John O'Gallagher. Born 1735 in Ballyshannon, Donegal. Immigrated to USA with 2 sons (Jamesand Hugh). Died 1792 inDublin Township, Huntingdon County, Pennsylvania, USA. My 3rd Great grandfather was James Gallaher (name changed perhaps when he came to USA). Born 09 MAR 1759 Killaghtee Parish,CountyDonegal, Ireland.DEATH 8 FEBRUARY 1854 Burnside Township, Clearfield County, Pennsylvania, USA. His wife was Margaret Ramsey who was borninHuntingdon County, Pennsylvania, USA1769 Huntingdon County, Pennsylvania, USA.DEATH 18 NOV 1840 New Washington, Clearfield County, Pennsylvania, USA. I do not know her ancestry. The information regarding John's wife was not totallyclear but may have beenNancy McAfeeBIRTH 1740 Ballyshannon, , Donegal, IrelandDEATH 1810, Ballyshannon, Donegal,Ireland. I am a novice at geneology searches, and have no idea how to go about looking for records, or graves in person. Any advice would be very helpful! Thank you! Christine Drommond (c.f.drommond@gmail.com if desired)