Doonasleen isn't one townland, it is 3. Doonasleen east 196 acres, Doonasleen north 526 acres, and Doonasleen south 600 acres.
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 the Murphy children with a father forenamed Eugene or Owen, I found some rcds, but those jump from county to county. This is uncommon among the Irish. I would have expected them to be in the same county and likely the same parish. Will let you chase these rabbits.
For Bri(dget) Breen B 1820 +/- 4 yrs, Co. Cork, with the father's forename unknown, I found 1 rcd in 1820. Father's forename was Thomas. Will leave it to you to visit the database and find the parish name.
For Bri(dget) Breen M 1841 +/- 4 yrs, Co. Cork, I found 0 rcds. They may have married elsewhere. From your indirect evidence, it appears they married and raised their family in Ireland.
For Eugene Murphy M ditto, somewhere in Ireland, I found 2 rcds: both 1841, Co. Cork. I'm surprised I didn't find a matching M rcd for Bridget.
For Eugene Murphy B 1818 +/- 4 yrs, somewhere in Ireland, with the father's forename unknown, I found 1 rcd: 1815. Father's forename was also Thomas. Ditto.
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.