I research the Irish Family History Foundation's database. It contains 12,000,000 surviving rcds for abt 65% of Irish counties. Rcds are increasingly sparse B4 1840, rare B4 1800.
Note 1 - Without a KNOWN county, the chance of an ancestor's rcds NOT being in this database is AT LEAST 35%.
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).
For Peter McKenna B 1869 +/- 4 yrs in Co. Louth with the father forenamed James, I found 1 rcd in 1869, Haggardstown RC parish.
For possible siblings B in Haggardstown parish with a father forenamed James, I found Ann 1883, Bridget 1879, James 1873, John 1874, Marg(aret) 1876, and Pat(rick) 1871.
For James McKenna M 1864 +/- 4 yrs in Co. Louth, I found 1 rcd in 1866, Dundalk RC parish.
For B???? Mullen M ditto in Dundalk RC parish, I found 1 rcd. This is a match. The rcds are HIGHLY likely to be for your ancestors. A view of the detailed rcds should show whether they married each other. If so, the rcds SHOULD show their parents' names and other info.
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.