Hi Kathleen
Yes you have indeed been some help. For example I hadn't picked up on the 1930 Kalispell directory showing L E Denning as a separate entry to Darwin Emery and Lillian E. That is surely too much of a coincidence to be two different people and gives some weight to your idea of them living together and passing as married.
All of the other information is useful in that it confirms my own findings, including the second marriage of Darwin Emery to Edna Kendrick after the death of Lillian in 1939.
With regard to Darwin registering for WW1 in Nebraska that is very interesting too. Sarah actually died on the 4th October 1917 which explains why Arbey Emery is named as his next of kin. On the 1921 census Arbey is aged 41 so he must have been a brother. This tells us that Darwin went home fairly soon after the funeral and if the 1921 census is to be believed he then returned to his farm in Claresholm after the war ended.
It doesn't help to explain his state of mind in naming Sarah and the two children as living with him though !
In her letters home Sarah named a local farmer named Gordon Algar McRae as the father of Victor Gordon and we believe from other letters received after her death that Sarah was born as the result of an attack/rape.
Thanks again for your interest and kind help.
Brian