You can use a displacement map to slim down the edges of an image to counter the wide angle distortion. Open your image and create a new layer and fill it with 50% gray. Hit "D" to reset your fg & bg colors. Select the gradient tool and set the blend mode to darken. With black as the foreground color create a gradient from the left edge to about 1/3 the way in the image. Hit "X" to reverse the fg & bg colors. Change the gradient tool's blend mode to lighten and create a gradient on the right side as shown here.
save the image as a psd. Turn off the visibility of the gradient layer. Put your group shot into a smart object so that you can readjust it if you're not happy with the results. Use Filter>distort>Displace. It will bring up a dialog box asking for the horizontal scale and vertical scale. Set the vertical scale to 0 and play with the settings on the horizontal scale. Try the default first and change it if it's too much or too little. When you click okay it will ask you to choose a file. Select the saved version with the gradient visible. Here's an example - not a good one for fat people on the ends, but it's all I have handy at the moment. First image is the normal image. The second is the one with the displacement map. I over exaggerated the result to show how it works better. There is also some edge that you'll need to trim off.
