Jo K,
McGuire/Maguire (after which Maguiresbridge is named) is the most common name in Co Fermanagh. They were the ancestral Irish landowners in that part of Ulster. The majority would have been Catholic though.
Tradition was to marry in the bride’s church after which she’d attend her husband’s. So if she was Church of Ireland and he Presbyterian you would expect a marriage in the Church of Ireland but afterwards the children would be baptised in a Presbyterian church. Not every family followed that rule though.
In a mixed marriage ie Catholic - Protestant, each family came to their own arrangements. Sometimes one of them changed lanes and adopted the other’s denomination. In others you see the sons brought up in the father’s denomination and the daughters in the mother’s.
I would definitely check the Clogher Church of Ireland records. Many Scots settlers did end up Church of Ireland especially in Fermanagh and parts of Tyrone. This is because many of them came from the Scottish Borders where Presbyterianism hadn’t arrived at the time they left. It was pretty lawless in the Scottish Borders until the 1630s and essentially they had no religion then, marrying by handfasting for example. So they came to Ireland with no religion and settled into the Church of Ireland rather than Presbyterianism. (They were known as Border Reivers. See link below). The Presbyterians who did make it to Fermanagh and Tyrone tended to come from further north in Scotland.
According to MacLysaght’s “The Surnames of Ireland” McClintock is: “A Scottish name numerous in Antrim and Derry. Black says this, like MacClinton, refers to St. Fintan.” (Black is the acknowledged expert on Scottish surnames). Of Houston, MacLysaght says: “A well known Scottish name very numerous in Ulster. It is sometimes a synonym of MacQuiston, and in Donegal of MacTaghlin.” Of Maguire he says: “The leading sept of Fermanagh. Many members of this sept have been distinguished in the history of Ireland.” Of MacDowell he says: “This is the Irish form of the Scottish family of MacDugall which came from the Hebrides as galloglasses, and settled in Co Roscommon where Lismacdowell locates them. It is now mainly found in north Ulster, largely due to more recent immigration.”
Galloglass/gallowglass were mercenary Scots who were brought to Ireland in the 1300s and 1400s to fight for various Irish tribes (who were always squabbling with each other). In return for their fighting skills they were given land by the local Chiefs. Some eventually went home to the Hebrides but many settled in Ireland. Their descendants would tend to be Catholic because they arrived pre-Reformation. MacDowells who were Presbyterian or Church of Ireland tend to be folk who arrived from around 1610 onwards when the Plantation started.
Incidentally, in Ulster, McDowell is often pronounced Madole or Medole, and you do see those spellings too. Mostly in Antrim and Oriel, according to MacLysaght. Oriel is the area around modern Co. Louth.
https://en.wikipedia.org/wiki/Border_reivers