It is going to be incredibly difficult to get two people , in the same light, to be that many stops apart just by virtue of their skin if you're correctly expos

It is going to be incredibly difficult to get two people , in the same light, to be that many stops apart just by virtue of their skin if you're correctly exposed. If you're under or over exposed, someone might clip out sooner , but a well exposed image will have enough latitude to capture both.