Those shutterbug dads with all the FABULOUS photos of their cute kids can be the real portrait "challenge". We had one of them come through our lives in a whirlwind a few years ago, and he left photo albums and shoe boxes full of snapshots all over the place, an archivist's nightmare. (FABULOUSLY cute kids, though.)
Part of the challenge is that Dad imbues the photos with a lot of background information and emotion to which the objective viewer won't be privy, but Dad will expect the finished painting to capture all that.
And there's the hazard. Given your brief observation about the father, I rather suspect that you could produce this photo in oil with absolute fidelity and that he'll think it falls short -- because he doesn't realize how the photo falls short, not necessarily as a photo (though it does), but as reference material for a fine art portrait. Our eye will usually "forgive", or at least supply, missing information in a photo, but every decision in the painting will be regarded as deliberate and executed as intended.
They've further hamstrung you by requiring that your work fit the frame they have, so "cropping" solutions will be a bit more difficult to implement.
If you decide under the circumstances to have a go at this and see what can be made of it, you might take some time to browse through the SOG galleries to try to spot similar presentations and see what distinguishes them. (I'm thinking largely in terms of orchestrating contrasts, and in creatively handling "white" clothing.) I'm also put in mind of Lon Haverly's
Oil of Mariah from Forum days of yore.
Cheers