Hi Jamal, 

Have you considered practicing 3 shooting individually just to ensure the right technique is used and players are comfortable before introducing 3 shooting in a game like situation. 

Here is a drill for jump shot positioning which should help players get into right position before releasing the ball Jump Shot Positioning.

Even though this is a free throw shooting drill the same principle can still be applied, just may need to add a bit more of power in the shot Free Throw Shooting Technique

Hope this helps, let me know of your progress.

All the best.