June, July and August are normally the warmest months in Scotland. The temperatures in Glasgow, specifically, in August are usually low and can range between 59-63 °F. It has been said that you can expect rain for roughly half of the month of August in Glasgow. So, just a head's up, we might encounter some rain :)
I would recommend that everyone watch the following video. It shows you a 360 view of the surrounding terrain. http://www.oldcastlelachlan.com/project It's about a 5-10 minute drive out to the Old Castle, depending on your lodging. And from where you are able to park, it's about 2 minute walk out the actual grounds where the ceremony will be.