Welcome to Ireland Reaching Out!
Your ancestors are likely from Tullaghobegly civil parish in northwest Donegal. The RC parishes for Co. Donegal start very late compared to other parishes across Ireland. Gortahork records start in 1849 and the other nearby parish, Gweedore, has records starting in 1868. Just to be sure, I did check the subscription site Roots Ireland for a baptismal record around 1847 for Denis or Margaret with a father Edward but got no record. There are many, many McFaddens in that area. One of my great-grandmothers was a Catherine McFadden from the next civil parish to the north and east-- Raymunterdoney. She emigrated to Philadelphia in the late 1860s.
Have you had your DNA tested? You can also add the McFadden emigration story to our XO Chronicles site https://www.irelandxo.com/ireland-xo/history-and-genealogy/ancestor-data...
Let us know if you decide to come to Ireland this year.