Carman;
Have found some more information regarding the battle for Courcelette on 15 September 1916, where your Grandmother's two cousins were lost.
Part 1:
The below links concern the 27th Canadian Infantry Battalion, C.E.F. of which Private Archibald James Viznaugh was a part of. These pages are from the 27th Bn's War Diary for Sept 1916:
War Diary entry for 15 Sep 1916 - page 1
War Diary entry for 15 Sep 1916 - page 2
Operations Order of 14 Sep 1916
Operations Order of 15 Sep 1916 - page 1
Operations Order of 15 Sep 1916 - page 2
Operations Order of 15 Sep 1916 - page 3
Operations Order of 15 Sep 1916 - page 4
After Action Report for 15 Sep 1916 - page 1
After Action Report for 15 Sep 1916 - page 2
Summary of Operations 7 to 15 Sep 1916
Thought you'd find these of interest.
Cheers
Part 2 to follow