I have a lot of info on the Markinch Bruntons who were pretty much all related at one time or another. Don't know exactly where your family might fit in or when your Uncle was mistaken for 'George Brunton who lived in Markinch'? I do know that two of my great great grandfather's brothers were born in Markinch but went down south to farm in the 1870's, they were David and George and each had a son George. Both of these sons ended up back in Markinch for a bit at least and one of them could have perhaps ended up in the Dalkeith area as his mother moved from Hertfordshire to Edinburgh after his father died young in 1884. My great-grandfather also had a brother George who lived in Markinch for quite a while although he eventually emigrated to the States. As far as I known, there aren't many Bruntons left in Markinch now though I grew up only 5 miles away and have full details of all of the descendants(100's!!!!) of my great grandparents as well as pretty full info going back another 3 or 4 generations and some sketchy stuff from before that. Even if there is nothing which helps you in the my great-grandfather's generation, I may have something from previous generations which you can tie in?
Contact me if you would like me to send you what I have my direct e-mail is firstname.lastname@example.org