Okay, contrast and brighten are only going to do so much. They'll make the image darker while brightening everything AROUND the figures, basically. What you want to do is use the "screen" option. First, in photoshop you go to "LAYER - DUPLICATE LAYER." When the next layer comes up, go to the right-hand sidebar and look for where it says "NORMAL / OPACITY 100%." You have to open the box and it'll give you a ton of options. Darken, Brighten, etc. Choose SCREEN. This will instantly make your image lighter, but sometimes it'll be too pale so you need to adjust the OPACITY. If it's still too dark, though, you can just duplicate the SCREEN layer again and it'll go even lighter. Keep doing this until you achieve what you want.
After that, you do to it like you would any other image. Adjust the levels, brighteness, contrast, sharpening. You should get a pretty decent image.