Okay, I think I have your answer to charcoal / sand separation.
After you have separated the water and dissolved sugar using a filtration setup, allow the charcoal and sand to dry.
Now put the charcoal and sand mixture in a beaker and add water (enough as you see fit).
Swirl the mixture a little and the charcoal should float to the top of the water while the sand settles to the bottom. Now you can decant off the water with charcoal. Continue to add water and do this until all the charcoal is removed. Now just filter the water with sand again to remove the water, let the sand dry, and that should be it.
I'm assuming the charcoal is broken up and not in very large pieces? Try this.