Presume this is the headstone
"
Erected by P. Hayes, J.P., The Oaks, St. Leonard's, Sydney, in memory
of his Father John Hayes, who died 18 April 1858, 63 years. R.I.P.
[An upright stone."
Assuming they were RC. then Leighlinbridge parish office would be your best bet for marriage and baptismal details.
Contact details should be easy enough to find.
http://www.leighlinparish.ie/(think I posted them on a thread in Carlow forum last week).
As regards census records ;no nothing for Ireland until 1901. You could try Griffiths Valuation but that will just give the householder/landowner and address but no details re. other people in the house.