Hi bupski,
We are related!
Michael Keegan and Esther Clarke are my ggg-grandparents through their daughter, also Esther, born in 1860. I had only done some preliminary research into them, so this information is from my notes from last year.
They were married in 1844 in Kinnegad RC parish and I have found 8 children, including your ancestor, Elizabeth (the last), in 1864. There are a good few Keegans around Kinnegad/Killucan area, so I have not definitively narrowed down our Michael Keegan's address. There are 4 possible townlands for Michael Keegan in Griffith's in the civil parish of Killucan:
Aghamore
Derrymore
Kinnegad
Riverstown
The birth certificate for Elizabeth may give us the correct townland, but I have not acquired it from the GRO yet (it's still on my todo!).
Esther, my ancestor, moved to Dublin and married a Peter Coyne, a train driver. Some of the rest seem to have ended up emigrating to Newport, Rhode Island (Francis, Margaret and Mary). I had found Elizabeth's marriage to Edward Walsh in the index, but did not get the record.
As for what happened to Michael and Esther (snr), I have some possible death records from the civil registration indexes, but have not followed up on them. Once we have the address, that may lead us to the correct graveyard.
Going back further may be possible with records from the Tithe Applotments and deducing relatives from the marriage record witnesses and children's baptisms, but it's tough to say at this point.
Sure let me know your information and see if we can piece together some more details.