Here is part of a message from my niece, Fiona Fraser. I have looked at this website, and it is very easy to find John and Jim Buchan. It's desperately sad to read about them, how much harder must it have been at the time? Fiona's dates are correct.
Anyway.
Hi Kirsty
....
I was reading the BBC History magazine and came across a very interesting
website address, the Unofficial War Graves Watchdog. I've just been having a
look at it to see if I could find out about John and James Buchan, and they
are on it. The web address is www.cwgc.org All you need to do is put the
surname and initial in and which war they were in and it gives you a list of
names. I don't know if you have the exact dates that they died, (there are
many "J Buchan" s on the list), but they are James Buchan 20/07/16 and John
Buchan 17/05/15. It's all very sad, I don't think James Buchan has a grave,
only a memorial. Anyway I thought this would be interesting.
Hope that website is of use to you and see you soon.
Fiona
If you don't have time to search, I have copied the relevant pages below.
This is a picture of men in the trenches at Thiepval Wood, where James Buchan is listed on the memorial.