Based on a quick Internet search, the difference between “naíonra” and “naíolann” seems to be that the former is a “playgroup” (usually an Irish-language one) attended by children for a couple of hours a day, whereas the latter means “crèche” where children are looked after throughout the day. As regards “reiligiúnach” and “reiligiúnda”, I wouldn’t be able to help you, but in many cases Irish uses other words for talking about religion, e.g. “cúrsaí creidimh” (religious matters), “duine cráifeach” (pious/devout person), “leabhar diaganta” (religious book).
