I've got grenades working. I was originally using primed TNT to spawn when a snowball was 1 block above the blocks used in the map but without a gamerule to disable TNT griefing I had to change the TNT to a primed creeper. The only problem i'm having now is that for a split second before the snowball explodes, you see the creeper. I've tried using the invisibility effect tag but you still see the creeper and it just leaves a lingering invisibility effect in the area. I was using this code but I disabled the invisibility effect due to the reasons listed.
Added screenshots for those of you that hate videos. This photo of endor is just a quick update. In the final result there will be much more foliage and buildings such as ewok tree homes and imperial bunkers.