Unfortunately, the pre-1877 records for the Church of Ireland church in Lucan were destroyed in the 1922 Public Records Office fire in Dublin. So there would be no baptismal records for any Coley or O'Brien children baptized in that church pre-1877. Civil registration of Church of Ireland marriages started in Ireland in 1845. I can't find a marriage record at the free site www.irishgenealogy.ie so my presumption is that Elizabeth Coley and William O'Brien married prior to 1845.
Have you considered DNA testing? Maybe you will have matches with descendants of Cornelius O'Brien or Edward Coley.