Have you tried checking the land records called the Tithe Applotment Books (1823-38) or the later Griffith's Valuation (1848-64) for relatives of James & Mary?. The Tithe Applotment Books (1823-38): Microfilm copies of the books for all of Ireland are available at the National Archives of Ireland (NAI) http://www.nationalarchives.ie/genealogy1/genealogy-records/tithe-applotment-books-and-the-primary-griffith-valuation/ or the Church of Latter Day Saints (LDS). Griffith's is freely available here: www.askaboutireland.com or here: www.failteromhat.com Failte Romhat has lots of other useful links you could try looking at.
You may try contacting Brian.Mitchell@derrycity.gov.uk for further genealogy assistance.
All the best.