Need info on Anthony Barrett and Mary Hanlon

I've been researching my Barrett clan Irish roots and have managed to get as far as my great-great-grandparents who were from Ireland, got married, and immigrated to American and settled in the Towanda, Pennsylvania area.  I've hit a brick wall here and can't get any further.

My great-great grandparents were Anthony Barrett and Mary Hanlon (O'Hanlon?).  Most of the solid information I have on them is from their tombstone (of which I attached a photo).  Anthony's death is listed as Sept. 25, 1885, age 65, so his birthyear would be approx. 1820.  Mary Hanlon (whose named is listed as Handlon on tombstone) died Mar 26, 1898, age 74, so her birthyear would be approx. 1824.  It says they are natives of Castlemagner, Co. Cork.

They had six children, born in Pennsylvania: Edmund D. (1854-1928), Thomas (1859-1940), Mary (1862-?), James Joseph (1864-1928), Hannora (1867-?), Patrick J. (1869-1954).  Their might have been another child (the oldest) that died on board the ship over.

I did find one file NLI online from the Cloyne Dioscese that showed an Anthony Barrett and Mary Hanlon got married on Feb 25, 1848 with witnesses listed as John Burke and Margaret Hanlon and a residence listed as Gurteenbeha.  Mary Hanlon's mother was supposedly a Burke and kin to the famous Edmund Burke, so that might fit.  Other than them being Catholic, this is all I've got.

Basically I would love to find out who the parents and siblings of both Anthony Barrett and Mary Hanlon are, so I can advance the genealogy ball a little further down the field.  I'm hopeful that I might get a better idea of the Irish side of the story and maybe even discover any distant family we still have there and get in touch.

Any information you can give me on my search is greatly appreciated.  This website is a wonderful idea.  Thank you.