Moving to Chesham

Hi there, we currently live in Ruislip and are considering moving to Chesham for a better quality of life and schools. My knowledge of the area is very limited, we are at the infancy of our research. We have an 8 year old and a 5 year old, a boy and a girl. Ideally, we would love to get them into either Dr Challoners or Chesham Grammar. I have no idea how competitive these schools are, even once you are in catchment. Do they both have the same catchment areas? Another question is what areas should we be looking at for a home given that we have our eye on these schools? Any areas to avoid as we have a young family? If anyone has any additional insight they can offer, I would be most grateful. I am feeling slightly anxious at the prospect of having to deal with multiple moving parts! Husband and I will likely have to commute to London once or twice a week. Thanks so much, in advance.