Janet,
Statutory registration of marriages started in Ireland in April 1845 (save for RC marriages which were only recorded after 1864). So Adam & Mary?s marriage was before that date and you won?t find a statutory marriage certificate for them. You might find the marriage in church records but to do that you usually need to know where it took place. (Tradition was to marry in the bride?s church).
Death (and birth) registration didn?t start till 1864, so if Adam died before that, you won?t find a statutory record of his death.
I looked at the Braid website which lists gravestones in the Ballymena area, but there are no Loudon/Loudens there at all. Indeed looking at the 1901 census it doesn?t appear to be a common name in that immediate area. (It was found a little further north nearer Ballymoney). There weren?t any Kinloch gravestones either. How sure are you the families came from Ballymena?
http://thebraid.com/genealogy.aspx
If Mary married Edward Porter between 1853 ? 1861, and it wasn?t an RC ceremony, it should appear in the Irish stat records but I cannot see it. Nor can I see a marriage for them on Scotlandspeople site. Did they have any children born in Scotland in 1855 or from 1861 onwards? If so, the children?s birth certificates will record the date and place of their marriage.
I see a death on Scotlandspeople for Mary Porter in Bo?ness in 1903, aged 82. Previous name is Kinloch. I assume that?s Mary?s death. It?s always worth checking all Scottish censuses to see if an exact place of birth is given. Sometimes you get more than just ?Ireland.?
If you can?t find the date and place of the 2nd marriage from birth certificates, but you are sure the children to the first marriage were born in Ballymena, you could search the church records for that area to try and trace the family that way. I suspect they were Presbyterian or perhaps Church of Ireland. Not all the records for those denominations are on-line. Copies are held in PRONI (the public record office) in Belfast. However a personal visit is required to access them.
Elwyn