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).
For Rosanna Johns(tone) B 1829 +/- 4 yrs, Co. Cavan, with the father's forename unknown, I found 1 rcd. However, the father's forename was William. Any chance your info could be in error?
For Margaret Johnston B ???? ditto, with the father forenamed John, I found 1 rcd in 1834, Castletara, Co. Cavan.
For Maria Johnston B ???? ditto, I found 0 rcds.
For John Johnston M ????, Co. Cavan, the only feasible rcd within a reasonable range is for 1805. This seems to early for your timeline.
For Mary Murphy B ditto, I found 0 rcds matching the one for John.
With the mixed results above, it looks like their B/M events weren't rcd'd, or didn't survive. You may want to search other counties, or all Ireland, although this will likely muddy the waters with lots of false positives.
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.