Clear Island Parish in the Poor Law Union of Skibbereen.
for church records
this is the only online records for the South-East of Cork, hopefully you will find some there. There is a genealogy office for this area too.
If you wish to have copies of birth certificates after
1864 you can get these through the websitewww.groireland.iewww.familysearch.org
spotted most of the children's names on this website
with their civil registration births but no parents names listed with these.
eg: Patrick Oct-Dec 1898, Skibbereen
Hanora and a Honora and a Hannah
Ellen July-Sept 1892
Florence Oct-Dec 1900
Mary Kate Sullivan April-June 1897 Skibbereen
Vol. 5, Pg. 472 #4193980
there is a match with a Patrick Fitzgerald but no further details. Usually a marriage record comes with only the father's of the bride and groom.
In 1853 there was a valuation of land for taxes it was called the Griffith Valuation. At that time there were 1,021 Fitzgeralds and 5,414 Sullivan's in Cork.www.askaboutireland.ie
Too early for your families but you and see the grandparents or great grandparents.
In 1853 is Edward, Garrett, Stephen & John.
I looked in the Cork Directories, there are a number of Thomas FG but none in Skibbereen.'
Thomas, farmer Ardnageehy
Thomas, farmer Whiting Bay
There are others as well but most toward Cork City, Lismore Cappoquin a grocer and Modelligo Farmer.
The numbers of both Fitgerald (700) and Sullivan (124) in the current phone book sort of rules out letters. However, I did not go through these looking for the Skibbereen
Carberry West. If you have a good map you could match these up with the area. Too much work for me, needs a family person.