You are courageous and brave. It is the right thing to live a good life according to your conscience.
It is very tough and unfair to be shunned by parents. I am df'd but my parents treat me the same as before, because they don't approve of the shunning teaching.
Of course you can defend yourself and try to show your family how bad the shunning is. But please do that with Love and not sarcastically. If you do it with love, it will heap firy coals on them to use Jesus words. It's also good to ask if Jesus would shun anyone.
Show them that you respect their belief but also that you like them to respect your agnosticism. Maybe don't argue with them about their faith. Chances might be good that they could change their views too.
If they attack you about why you left, you could just say that also are disillusioned because of the australian royal commission case. Don't explain everything... they have to research it for themselves.
I wish you a lot of joy and happiness in your life without the harmful wt influence.