In the top left photograph, I believe that, from left to right, are Lindsay, Bethune, Henderson and Stewart. Certainly in the lower left image, we can see Henderson (left) and Bethune, who are wearing the darker coloured jackets. Samuel Duncan is holding the club in the lower right image. It is more difficult to tell Lindsay and Stewart apart. If you can tell, please comment. If you are aware of any other images of David Milne Stewart, the long-standing headmaster of Lundin Mill School, please do get in touch.
Back in the days before emails and phones, Edinburgh-based Peter Henderson would send a postcard to William Bethune saying he'd be off the train at Lundin Links at 3pm with his golf clubs. Bethune would get his son to pass the message onto his head teacher (Stewart) when he arrived at school. On such days, the school may have closed early so that the eager golfers could be on the course by 3.05!
With thanks to John Band for the images and information