how to correct facial shadows from sun

Photos does not have any dodge and burn brushes to darken or lighten selected areas like Aperture or Photoshop.

You could try to to use the "Shadows" slider to selectively brighten the shows in the photo.

You could also use the "Brilliance" slider to increase the exposure while preserving contrast and detail. But Brilliance requires an upgrade to Sierra.

I have not yet found any bargain priced Photo Editing extension, that can touch up portraits well.

You could as well buy a very good editor like PhotoShop, Affinity Photos, or Pixelmator.

Pixelmator and Affinity Photos come with the a retouch Photo Editing extension.

A test with Pixelmator retouch, called from Photos: Trying to remove the shadow of the nose by inpainting - the original to the left, the retouched photo to the right.

The Dogdge &Burn brushes in Pixelmator retouch did not have any effect at all, also the smoothing brush, when I tried to smooth the border of the shadow.

Not really - you can play with the highlights and shadows sliders

and If you get up to date (you are nearly a year behind) with OS X Sierra 10.12.4 you have more and better editing available

and of course there are extensions you can purchase that may do better Photo Editing Extensions for Photos for Mac

LN