That is a good question. My theory: Looking at the lay of the land and the fact that they found a partially melted bucket with unburnt remains buried fairly deep, it makes sense that that the burning took place in the cemetery. Yes, there would have to be fuel (accelerant, limbs, and/or debris) to burn with it but because there were unburnt remains, the fire wasn't hot enough or didn't burn long and deep enough to completely destroy everything.
Logistically thinking, I just cannot not see them burning in the fire pit and then going through the burden of digging out and moving burnt remains, including the partially burnt bucket, to the burial site. That would take more time and work and create two areas to cover up. Besides, if they/he found the bucket partially burnt and had to move it, I'm sure they/he would have made sure that part of the job was complete or done something else with it.
AxC could have been there to assist in the dismembering, initial digging, hauling in fuel/debris and perhaps even the burning. AxC's cell pings and the time he was there helps support this theory but it's also possible that CD could have done the initial digging and then the burning with or without assistance. CD could have used a rake to gather and finish burning any limbs or debris so that could be the reason charred bones were strewn around somewhat. Regardless, CD finished the job of moving the dirt back to conceal the fire, using the so-called raccoon as the excuse for disturbed dirt in the cemetery. I doubt he would have left burnt debris and limbs in sight on the cemetery surface since that would have looked unnatural for burying a raccoon. Any unburnt limbs left on the surface at the cemetery could have been picked up with a shovel and thrown in the burning pit and unnoticeable.