William & Ellen were married in Carnone Presbyterian church on 7.4.1924. So not a civil ceremony. Both lived in Sessiagh Long townland, near Castlefin at that date. William was a farmer, as was his father James.
I don’t see him in the 1901 or 1911 censuses, though there was another Wm Alexander living there at the time, who died in 1922.
Ellen’s father was William Byrne, labourer. You have two threads running in your search for these families which makes things a bit confusing. In the other thread you have said that you think you have found Ellen’s family in Kilcasey in the 1911 census. That family has Patrick as head of the Byrne household. So given that her marriage certificate says her father was William, I’d say the Kilcasey family is not the right family.