Check out @Lindagaf’s thread on “the average excellent student”. There’s tons of good advice on there.
The problem with comparing your chances with your siblings’ experiences is that schools are getting more and more selective. That doesn’t mean that Georgetown and/or Duke are “out of reach” for you, but that you are facing a more competitive admission process than your siblings did and that you and your parents should be prepared for that eventuality. I know that’s hard.