Hi, I cannot tell you anything much, however I put the title of the photo into the internet and one of the only "Hits" to match anything like was an item on a auction site "*bay", this was titled
"RAF Flight "G" Squadron No.36 R & C Wing 1944" -Navigators Course Photographs.
so perhaps they could all have attended a navigators course and your Great Grandfather and the other two RAF men were instructor's?
Hope that's of some help.
Regards.
Frank.