I am pretty confident that he arranged everything, even directing the subjects where to look. Strand had been invloved in making films since working with Charles Sheeler on his movie Manhatta in 1921. He produced, directed and was cameraman on several films either for his own film company (Frontier Films) or working for the FSA.
Shooting a film requires a meticulous attention to detail to get the shot right.
I think those years of experience are evident in this photogaph.
I always get a feeling of push and pull in the image. A family pulled or kept together my the mother but at the same time straining to be seperate.
I think Don's comments fit with the idea of Strand not just as a photographer but also as an experienced director and film maker.