There isn't anything called hard A-levels. It is subjective to what you think. Doing the subjects you are good at is always the right thing to do and if you enjoy these 4 subjects, then go ahead with them. If you enjoy chemistry, I can assure you that it won't be as hard as people describe it. Challenging, yes because of the massive course content and how much you have to remember but again, I can say the same for biology, physics, economics etc. Just work on the subjects and never think you can revise and catch up later because in A-levels, you don't have much time to catch up. Work towards you goal and you will be fine.