I am thinking you want to know about the colorization basically. The people were selected out and placed on BG.
You're right.
Desaturate.
New layer. Paint a color in, such as the skin. Change blend mode to color and adjust the opacity to your satisfaction.
Make a new layer for each area you color. That way, you can apply different opacities, etc. You can also erase if you bleed over another color area.
New layer: you can lighten, even tones, minimize features this way: create a new layer, fill with 50% grey. Change blend mode to overlay. Select dodge tool and lighten areas to give them flat, almost cartoonish effect. Use a soft brush, low exposure. I start with midtones, this is usually enough since I'm not looking for that exact effect. But you can finish detailing with the other range settings.
If you want to emphasize something like Barclay's tie, then don't change the blend mode or try a blend mode of vivid light, etc. Experiment.
Okay, there are certainly more steps and techniques other members can offer. This is the simple way I would do it.