Thin crust pizza on barbecue
The secret to getting a thin crust is... use less dough. It's that simple. Pizza dough is flour, water, salt, yeast: there is no magic ingredient that will make it thinner. Simply use less dough per pizza. You may find that when you first shape the dough it will try and spring back. In this case, just cover it and leave it for 5 minutes for the gluten to relax.

As for the charcoal grill, there is no reason why a thin crust pizza should be done any differently to any other pizza. It's entirely doable.