You will not be able to get a flat tone or the same tone across each of their faces. Because you took the picture with a hard light hitting the one side of their face, it can not really be changed too much. You can play with it in the Camera Raw filter, but you will not get a cohesive tone across the faces. Usually before I do a shoot somewhere I go with an assistant to the location to do a sunlight test. See where the sun falls on a person the day before I want to do a shoot (at the same time of day that I have planned to do the shoot). If the sun is too bright then I will try to do it at a different time. Granted there are variable like cloud cover that can change the lighting. If I am not shooting up into the sky then a a day with a few clouds is perfect as it will filter the light better. If not then I bring a reflector to bounce light on my subject's face. Granted with a group... bouncing light is probably not that easy. I am guessing this photo was spur of the moment. Which is ok. You created a natural group picture that looks good. The overall tone of the image just needs tweaked. The hard light is ok for this shot, unless you are planning on using it for a team shot for a company website.... then I would reconsider redoing it. But alas, you can not remove the hard light perfectly from the side of their faces.
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