A marriage certificate might help if there is one. Given Ann the eldest ( my ancestor) was born 1842 I would say John b c 1818 and Catherine were married c 1840/ 41.
So far I have not found any marriage record but have read that many records have been lost in a fire or due to orders to destroy by certain authorities.
Civil registration of Catholic marriages began in 1864 and other marriages from 1845- before those dates there were no marriage certificates. No civil certificates have been lost.
Earlier marriage records (not certificates) were kept by the individual clergy and some may no longer exsit for a variety of reasons. Some Church of Ireland registers were sent to Dublin for 'safe-keeping' years ago and they were destroyed in 1920s.
The information contained in church marriage records vary greatly according to religion, date, church and that particular clergyman- some only list date of marriage, name of bride and groom and names of 2 witnesses.
