Welcome to Ireland Reaching Out!
Very glad you had a great trip to Mayo and Ireland. As you likely know the Killedan baptismal records do not start until 1861 so we can't locate the baptismal records for any of the children of Dominick and Bridget. http://registers.nli.ie/parishes/0135
I checked the 1855 Griffiths Valuation head of household listing for Killedan parish and the only Roach was a Thomas in Kiltimagh.
Do you know if Dominick was deceased by 1855 or possibly he was not leasing land? I assume he had not emigrated since his children left in 1864.
Have you considered autosomal DNA testing?