Help - Adjusting for Backlit

I took photos at a family reunion under a pavilion at a park on a bright sunny day. The "outdoors" portion of the picture was a nice high contrast good color. Unfortunately, the people in the shade part just don't have the color and brightness I want. If I adjust for the faces, I blow out the outdoors.

I've spent a few days with Gimp trying to learn about how to mask or select to make adjustments. I thought I could somehow select the bright outdoor portion of the pix, create some kind of mask with the selection, allowing me to adjust the portion of the photo of the folks under the pavillion, then finally add back the bright, colorful outdoors.

Does this sound right?

Anybody know if a tutorial to do this is posted anywhere?