Difficult, may have been adopted though the church, may have been a family member. lots of options
adopted parents are,
they crossed US border in Dec 1920, from Grand Forks BC, going to Rupert Idaho
Arthur Wellington Thomas 49 who became US ctitzen in 1939
Della Beecher Thomas 43
Robert Arthur Thomas 9
Ruth Lucille Thomas 6
Edith Della Thomas 4 who became US citizen in 1941
1916 census does not say she was adopted.
wonder if Lydia Witherspoon who is their cook,
living with them, is the mother???