I was interested to know where your Thomas came from because I saw that he had a son Owen O'Brien.
This name is very popular in my branch of the O'Brien family (who came from County Armagh). I have been searching the Internet to see if I could find any connections and I was interested to see that most Owen O'Brien's that I found came from around the same area of the North of Ireland - Counties Armagh, Monaghan, Louth and Cavan. I think there might be a connection between these. The name Thomas is also features in my O'Brien tree.
Here is the information that I have on my branch -
1.Owen O'Brien married Mary McAllister about 1800. Children: Owen O'Brien >>2 Michael O'Brien John O'Brien
2. Owen O'Brien married Bridget Finnegan about 1830. Owen and Bridget both buried at Drumintee, County Armagh.
Children: Michael O'Brien born 1833, Drumintee near Newry, County Armagh - married in Australia. John Joseph O'Brien - married in Australia Thomas O'Brien - married in Australia. Margaret Bridget O'Brien - married in Australia. Mary O'Brien - remained in Ireland, married. Hugh O'Brien - remained in Ireland, married, buried Drumintee.
Michael O'Brien was my GG Grandpa. I am descended from his son Owen.