It's note worthing that pre-Norman Ireland had a tenuous relationship with the Catholic Church, which was used as a pretense to invade it. So I think it would be more realistic to have them follow Insular/Celtic ChristianityOferlander
• Language: Oferlander Anglish (a dialect of Old English with Irish Gaelic loanwords).
• Ancestry: Northumbrian Anglo-Saxon, with Irish and (some) Cherokee ancestry.
• Religion: Western Rite Orthodox Christianity
• Culture: A communitarian, clannish system centered around tight-knit familial units incorporating aspects of Anglo-Saxon and Irish culture. They maintain a runic alphabet and have their own leader, titled a “Cyning.”
• Space: The modern Appalachian Mountain range, concentrated in the southern region (Kentucky, West Virginia, Tennessee, etc.)
History: The most commonly accepted theory about the ethnogenesis of the Oferlander people is that the group is descended from a group of Anglo-Saxons from the old kingdom of Northumbria who fled the area at the time of William the Conqueror. After first settling in Scotland, the tribes migrated to Ireland where they settled amongst the Irish clans, eventually being recorded in Irish historical annals as “Christians of Saint Cuthbert.” Most peculiar of this ethnoreligious group is their rejection of the Papacy following the Schism of 1054, placing them among the Eastern Orthodox churches in Constantinople and Russia.
During the English conquest of Ireland, the so-called “Irish Saxons” became something of a intermediary group between the conquering English and the native Irish, though their religious inclinations led to conflict with both groups. In time with the settlement of British America, the “Irish Saxons” began a mass migration to the New World and settled in the craggy hills of what they called “Oferland,” but would better be known as “Appalachia.” It was during this time that one Phillip Ludwell III would hear rumors of those in the mountains who carried on the legacy of “Orthodox Britain,” and sought the sect out. It was through his contact with the clans that the Russian Church would further contact them, eventually receiving the disparate tribe into communion with the formal church, even ordaining them a “Ethnarch” to serve them specifically.
The clans eventually would crown a King following American Independence, a war veteran who had taken part in the Battle of Yorktown. This would establish a line that would recognized as equal to Indigenous chieftains, and would serve as a rallying point for the Oferlanders in times of distress.
By the present, the Oferlanders have established themselves as a semi-sovereign nation within the borders of the United States. Thanks in part to lending their men to fight in America’s wars and spearheading the fight against the Coal Barons in the mountains, the clans have become a staple of America’s cultural patchwork, and have heavily contributed to the unique cultural identity of the Appalachian mountain region.