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 parish, 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 John Sheehan B 1844 +/- 4 yrs somewhere in Ireland with the father forenamed Maurice, I found 3 rcds: 1843 Cork, 1844 Cork, and 1846 Limerick.
For Maurice Sheehan M 1840 +/- 4 yrs somewhere in Ireland, I found 9 rcds: 2-1836 CRK, 1837 38 39 LIM, 1941 CRK, 2-1841 LIM, & 1844 CRK.
For Cath(erine) Keefe M ditto, I found 60 rcds. Only the following are potential matches with those for Maurice: 1836 CRK, 1837 LIM, 1841 CRK, 1841 LIM, & 1844 CRK. Will leave it to you to see if there are matches at the parish level of detail.
For Hanora Scollard B 1844 +/- 4 yrs somewhere in Ireland with the father's forename Nicholas, I found 0 rcds. In fact, I can't find rcds for these criteria anytime, anywhere in Ireland.
For Nicholas Scollard M 1840 +/- 4 yrs somewhere in Ireland, I found 0 rcds. Without a rcd for this name, it is futile to search for Catherine McCarthy
I conclude that these events occurred in a part of Ireland that hasn't been digitized yet, likely Co. Cork.
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.