haha it's interesting your parents are worried about bullying and the teaching quality.
1. bullying is basically non-existant in the top ranked selective schools.. honestly would think private schools have more internal issues with bullying.
2. teaching quality is subjective. it's most definitely not true that teachers slack off at selective schools because students go coaching. although they may not give the most significant help, i dont think its a valid argument to say they slack off and not fulfil their role...
3. this may be more personal, but if your family is able to financially support you going to a private school, it could have been an option to go to a selective school where it is academically safer and direct the remainder of the "school funds" i guess to your coaching/tutoring side of academics. once you hit yr11/12 and are quite serious about academics you will end up seeking out extra help. even though it may be "easier" to rank 1 internally, for the actual HSC you would be going up against everyone else in the state.
but hopefully you do come to a decision after deep consideration because there's a lot of things to consider changing from priv to selective but yeah just some thought ^^