I am from Cahir and have been attempting to trace my own family tree. When I saw your request for information I attempted to use The FAMILY search.org to investigate Benjamin Lewis from Cahir.
The information established was as follows: Benjamin arrived in NSW on the ship named 'SUSAN' on 25 March 1841 . His parents are listed as John Lewis (clerk ) and Catherine Rourke. He was accompanied by his sister Sarah Lewis (houswmaid) who was two years younger and was in his care. However, on Sarah details from the 'Susan' both parents were dead in 1841.
I have then a record of a Catherine Lewis (born circa 1831) daughter of John Lewis being married in Caher to a John Watts on 02 January 1851.
Then there is a record of the death of a Deboragh Lewis Stackpole in Boston,Suffock,Massachusetts on 25 September 1902. Deboragh parents were John Lewis and Catherine Rourke from Ireland. It is estimated that her birth year was 1823 ,very close to Benjamin and Sarahs. Deboragh's spouse was Byran Stackpole and she was widowed before her death. Her residence at time of death was 291 Western avenue, she died at Long Island Hospital.and her place of burial was Evergreen.
Some of the above probably confirms what you already know but I hope it will assist you in your search.