Hi Greg
A pleasure to help you out. I checked rootsirland.ie and there doesn't seem to be a marriage record for Thomas and Mary. It could be that the couple were married in a parish and at a time before records began. You could contact the church if you wanted a copy of the original baptisms of the children though:
http://www.irishmethodist.org/church/tandragee
I checked Slater's Directory for 1846 to see if Thomas is listed as he was a Carpenter but no sign of him. You can have a look here:
http://www.failteromhat.com/slater/0130.pdf
I also checked out Griffith's Valuation for Overend listings and there are a few recorded. I include the link below, you may see options there that I don't:
http://www.askaboutireland.ie/griffith-valuation/index.xml?action=doNam…
One additional thing to think about is the progression of the family name/others on any plot that might include above, potentially related ancestors on the Griffith's link I provide. If you look at these Griffith's entries in conjunction with the Valuation Books (a follow-on of Griffith's) then you may be able to chart which family stayed on the land or took it over up to the 1920s. For Northern Ireland these Valuation Records are available online here:
http://apps.proni.gov.uk/Val12B/Search.aspx
It takes a bit of time to get used to using the PRONI search and read the entries as they are digitised copies of the original but worth it as they are very interesting. You can find out more about them here:
http://www.irish-genealogy-toolkit.com/Griffiths-Valuation.html
Let me know how you get on - the above may or may not yield results
Best wishes
Clare
Genealogy Support