To me, the most important conflicts of these three chapters involve Johnny. One is between Johnny and another person (his mother) and one is between Johnny and nature (the fire and its effects).
I think that the conflict between Johnny and the fire and its effects is the most important. It is so important because Johnny is going to end up dying after his struggle and his struggle and death will have such a huge impact on Ponyboy.
The conflict between Johnny and his mother is important for similar reasons. It emphasizes what a tough life Johnny has had and makes us (and Ponyboy) sadder when he dies. It will also help lead to Dallas's death.