I know that my great-great grandparents came from Longfield as it was shown on the Catholic Diocese records in New Brunwick, Canada. Unfortunatelym I do not know if they were from East of West. How can I find this out?
The RC parish for Longfield encompasses both civil parishes (Longfield east and west). The RC parish name is Langfield. Their baptism and marriage records start in 1846. They are on-line free on the NLI site. See:
http://registers.nli.ie/parishes
If your family predates 1846, you could search the tithe records (assuming they had any land). Longfield West tithes date to 1826. Longfield East to 1829 and 1838.
http://www.cotyroneireland.com/tithe/titheindex.html
I see Kelly households in the tithes, in the townlands of Aughakinmart and Drumrawn, plus Russell in Curraghmulkin & Coolkeeragh.
Otherwise you may need to rely on DNA testing, if you are looking to match to anyone around there today.