I'm a Communication Merit Badge counselor too.
Our troop has a history of two scouts sharing the COH responsibility and I haven't changed things as this works well with two. I would not attempt it with more than two.
As for the campfire--there is nothing in the requirement that states there must actually be a fire. I had one scout who needed to finish up this badge. It was mid-winter, rainy, and the next COH wasn't scheduled for 3 months. I had him talk with the SPL about holding a "campfire" at the end of a troop meeting. We had skits, songs, and everything except logs. It was great fun and he earned #8.