I am researching the McCammon family, notably John McCammon, born and baptised in Clough, Co Down in 1853, parents William McCammon (address Carnacavill Maghera) and Margaret Mehaffey (address Moneylane Kilmegan) who married in September 1848, How can I be sure that William and Margaret actually were John's parents, and is there any way of knowing whether William is related to James McCammon, born 1815 in Co Down and who married Agnes Todd in 1854?
You don’t say what denomination the McCammon family were. But have you searched local church records for the baptism? (If the family were Church of Ireland then Clough’s early records are lost but if they attended some other church then the records may still exist).