Thank you all for your contributions, much appreciated.
Saddles - apologies, I neglected to mention the Mary had been married before she married Mr MacRae...it is the first marriage I am not sure if there was children from.
I will look in to the Olive Dunn marriage - thanks Radcliff. I have a feeling Farquhar may have been Edinburgh-based around that time, but he was with the army so he could easy be moving around with work.
Thank you for the death cert suggestions keyboard86 - can you tell me is there any way for me to investigate them other than writing to the specific registrar offices? As I say I'm fairly confident with Scottish research, but in the dark a little with how it works in the rest of the UK.
Thanks again.