Hi Elaine,
Yes, I think the parish registers record the reading of banns, not the actual wedding, which is why there are sometimes two entries, with slightly different dates, when the bride and groom attend different churches. However, your ancestors would have gone to that church, or a church which stood on the same site. When I was in Balquhidder, I walked from my ancestors' house to the kirk, along the path several generations of my family would have walked.
I am intrigued how you connect your John to Coilantogle, which is only about 50 miles away from the Atholl Estates, but would have been a journey of several days back then. Firstly, as I said before, it would mean that I have conflated two families, because of the baptism of another John in 1762. The mill at Blargarry is right next to Coilantogle, with Portnellan between the two, which is why I had assumed it was the same family. But their names are common, so it could be two different families with the same parental names. Looking at the dates, and not just the years, it looks like I am definitely wrong about the first John at the Mill of Leny. So, there is one set;
18/08/1751 Donald McLeran[McKinlay]/Mary McLeran John Miln of Leny Callander
Who is probably not even a MacGregor. Then. if your John is the Coilantogle John baptised 1758, there is another set;
20/05/1753 Donald McGregor/Mary McLeran Duncan Cullintogle Callander
01/11/1758 Donald McGregor/Mary McLeran John Cullintogle Callander
13/04/1760 Donald McGregor/Mary McLeran Margaret Cullintogle Callander
And then a third set;
08/03/1752 Donald McLeran [McGregor]/Mary McLeran Patrick Blairgarrie Callander
16/03/1756 Donald McGregor/Mary McLeran Janet Milntown Callander
30/09/1762 Donald McGregor/Mary McLaren John Milntown Callander
05/01/1766 Donald McGregor/Mary McLaren Daniel Miltown Callander
But I have to say, given the gaps in the dates, and the proximity of the locations, the two families above still look like the same family to me.
The second reason why I'm interested in your connection of John to Coilantogle is that by my calculation there were two other families of MacGregors living there for several generations. Both families used the alias of Drummond, after James Drummond, the 3rd Duke of Perth, who owned the estate until his death and the land seizures following the Jacobite rising of 1745. I think both families married women from my family tree, hence my interest. My family is the MacGregor branch of Dougal Ciar, or Glengyle, and they had a habit of marrying their cousins. So, the fact that the two families lived at the same location, and used the same alias, suggests they were brothers, or cousins. And the fact that they appear to have both married into the Glengyle family hints that they might also be from that family. But the only thing that connects them to your family above is the location. Although, they could have been siblings, or cousins.
I've already mentioned the McComas family, who lived near by, and may have been Glengyles. There was also a large family who used the alias Lyon, and lived at Blargarry. They also married into my family, but there is no obvious link to the family of Donald and Mary of Coilantogle.
I can give you more information about the MacGregors/Drummonds of Coilantogle if you think they might be linked, or even the McComas and Lyons, but I don't want to swamp you with data if there is no firm connection.
In the mean time, you may be interested in the Reports on the Annexed Estates, which details the confiscated lands and the lives of the people following the uprising. Coilantogle is in the Barony of Strathgartney.
https://www.chuckspeed.com/balquhidder/history/reports_annexed_estates.htm#_Toc189038803John.