Hi Pauline,
They are the same couple. What you call marriages are actually the posting of the marriage banns (intention to marry). It was very common to see the banns recorded twice, once in the parish of the bride and once in the parish of the groom. The actual marriage would normally be a short time after the posting of the banns and is often not found in the OPRs.
The actual entry for James and Christian on 25 July 1803 in Balfron reads "McLucky James in the Parish of Old Kilpatrick, and Christian Graham in this Parish entered their names for proclamation of Banns."
I don't have the image for the the July 29, Old Kilpatrick, Dunbarton entry but I'm certain it would be similar to the one above.
The same situation exists for the marriage of James McLuckie and Janet Archibald, on 08 and 10 Dec 1822 in St Ninians and Kippen, Stirlingshire, Scotland.
John