Hi Dianna,
I'm also looking into Patrick Gavin and his family. Patrick & Mary are my husband's 3x great grandparents. I have been a bit stumped as the shipping records give their place of origin as Barrowstown, co Kildare, and there is no such place that I can find in Kildare. I have been looking at the Tithe Applotment Books to try and find any trace of the Gavin, Burns, Lane or Tobin families in a small area. Your post alerted me to his baptism in Carragh, which I had overlooked.
All 4 family names are represented in the parish of Carragh in the Tithe Books (1820's - 1830's).
The other clue is that Patrick's nieces, Bridget & Catherine, who travelled to Australia with them have their place of origin as Thomastown, which is also in parish of Carragh.
Have you done any research into Catherine or Bridget? I have identified possible marriages for both of them in the NSW records, and it is possible that these certificates or their death certs may provide clues on the name of their father (Patrick's brother)
If I come up with anything else, I will get back to you.
Katrina