what if carol didn't really kill karen and david? maybe she's covering up for someone who killed the two?
most likely it's lizzie (the oldest of the little girls). she just did the burning of the corpse with the dismay of those creepy psycho little girls acting without her approval. going back on the previous episodes where carol's trying to teach them how to kill, how to survive and end their father's life. plus the way they killed them was sloppy and messy. we've seen how carol did and it wasn't like that. yes, there were scenes that rick was trying to re-imagine the killing, but the way carol answered rick's question if she killed was too quick as if she's covering for someone, the usual plot for that kind of scenes.