I research the Irish Family History Foundation's database. It contains 12,800,000 surviving rcds for abt 70% of Irish counties. Rcds are increasingly sparse B4 1840, rare B4 1800. Cos. Donegal and Derry were recently added to the database.
Note 1 - Without a KNOWN county, the chance of an ancestor's rcds NOT being in this database is AT LEAST 30%.
Note 2 - Only 1/2 of Co. Cork's rcds are in this database.
Note 3 - The RC church kept control over most parish rcds from Tipperary (north). These are ONLY available thru the Tipperary Family History Research center at a substantial fee (regardless of outcome).
Note 4 - Microfilms of parish church rcds are kept by the National Library of Ireland (NLI).
For Martin Kelly M 1848 +/- 1 yr, Co. Roscommon, I found 2 rcds: 1847 Ballinlough, and 1848 Boyle RC parishes.
For Cat(herine) Dolan M ditto, I found 2 rcds: both 1828. Neither is a match for Martin's. It looks like they married in America.
For Martin Kelly B 1825 +/- 4 yrs, Co. Roscommon, with the father's forename unknown, I found 6 rcds: 1821, 1825, 2-1827, 1828, and 1829. Father's respective forenames were Louis, Thomas, Malachy, Michael, Stephen, and Michael.
For Cat(herine) Dolan B 1827 ditto, I found 9 rcds: 1823, 1824, 2-1827, 3-1828, 1829, and 1830. Father's respctive forenames were Patrick, Michael, Patrick, Michael, Patrick, Malachy, Thomas, John, and Thomas.
For the B rcds, suggest you search the database and find the parishes associated with Martin and Catherine. If you find matching parishes for the two, this situation is slightly more likely to be for your ancestors.
Google the Foundation's name to lead you to this database. Register, opt to be notified as rcds are added and browse. Pls post your search results to my genforum msg.