So ... a few tips...
Even if you can't change cropping, you can change placement, so the guys that are cropped above the waist could be placed at the bottom of the poster and it wouldn't look so unnatural.
Avoid any solid color anywhere, even a two color gradient leaves you with a lot of solid.
I usually start with an image of fire, or vapor, or fabric or even something from the sport, like the ball or floor boards as a background base. You can also just use an otherwise throwaway blurry shot ... or a blurry blow-up of an area of bleachers crowd from your shoot.
Then overlay with a 4-5 color gradient (you almost always have 2-3 colors available from the uniforms ... black can also be used at the "ends" to create a dramatic vignette look)
I like to stay away from broken fonts like Stencil unless it's a special look (Army) or effect (sometimes use Crackle fonts) I'm after. Impact is something that is basic and solid and clear from far off. Varsity is also a handy font for school basketball. Again, avoid two-color gradients. You can even start with on of Photoshop's built-in multi color gradients, then tune the colors to your needs.
For the collage, use a broader feathering on your masking brush. The soft edges look .. well ... soft and a bit random. Make the photos larger so the overlap more, and use the masks to blend them together more. Don't be afraid of making some aspects of the images partially transparent.
Finally, try to do a little more with the logo. Left as is, it's pretty flat. A touch of layer styling (emboss, and drop shadow or outer glow) can go a long way to enhancing a simple logo.
This isn't really the same thing you're doing, but the example attached applies several of the concepts mentioned here. Hope this helps. Have fun!
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