There's always been a certain degree of inter-marriage in Ireland. Some families and areas are very relaxed about it. We have Catholic friends whose Presbyterian ancestor converted to Catholicism when he married and their children raised as Catholic. We have Protestant friends whose Catholic ancestor converted and children raised as Protestant.
One local Presbyterian man married (as his third, much younger wife) a Catholic woman. The marriage took place after they'd had over 12 children together (the whole lot being baptised Church of Ireland at the same time as the marriage).
Another local Presbyterian man married a Catholic woman and their children were baptised Catholic. The wife died when children were small and is buried in chapel graveyard. A short time later the husband remarried to a Presbyterian woman and the children were raised in that religion. One of the sons from the first marriage (baptised Catholic, raised Presbyterian) used to visit his uncle (the local priest) when he was in town.
My Irish great-grandparents had a mixed marriage- he was Presbyterian and her family were Reformed Presbyterian- which caused problems initially among some of her family even though they married in America. So, sometimes it just depends on the attitude of family and friends.