I got the photo off the net.
Look a the highlight on the back of his hand/wrist and compare it to the grandfather (... allowing for his darker skin).
His face might be in shadow, (see dappled shadows on wall.)
Another good point. The light on Dunham’s left hand across the tops of both of their legs and Obama’s hands are exactly right IMHO. The light logic on most of the rest of the photo works as well. But his head would have to be in a shadow to avoid the kind of light on top of his head exhibited in post #18 (admittedly more extreme than it would be in your pic).