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 Mary McAvoy B 1858 +/- 4 yrs, Co. Tipperary, with the father forenamed John, I found 0 rcds. Suggest you wait until the database is more complete.
For John McAvoy M 1854 +/- 4 yrs, Co. Tipperary, I found 2 rcds: 1851 and 1857.
For Ellen Hennessy M ditto, I found 2 rcds: 1850 and 1854. This is a NO match. Suggest you broaden the search to more counties.
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.