I found a few record but not the marriage record of James Clay and Charlotte Jebbitt.
First record was a baptismal record for Thomas which I located on the subscription site Roots Ireland
Thomas Kirkby Clay born April 19 1863 and baptized August 16 1863 Donnybrook Church of Ireland 3 Mulberry Terrace father James Clay mother Charlotte no surname
Then civil registration started in 1864 and I found tow birth records on the free site www.irishgenealogy.ie
William born July 24 1865 father James Clay and mother Charlotte Jebbitt eighth record https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_return...
Mary Kate born September 19 1868 father James Clay mother Charlotte Jebbitt ninth record https://civilrecords.irishgenealogy.ie/churchrecords/images/birth_return...