I fear that my parents will disown me if they come to know about it. I've quoted a few violent or illogical Quranic ayahs and Hadiths to make them think about Islam. Unfortunately, they either tell me not to think so much, or they think that it can't be as it seems as Allah knows best.
How can I tell them that I'm an atheist without making them hate me or disown me?
And how can I deconvert them from Islam too so that they can lead better lives and so that my younger siblings don't get taught Islam too (I'm the oldest sibling)?
The world needs more people like you: people who are seeing the folly and falsities of religions.
However at your age and in your circumstance as you've described, it may be better to not declare that you're an Atheist mainly because it sounds to me like there is a risk of it disadvantaging you severely and worse, have you persecuted for it.
You do not need to feel to convert people to atheism because atheism is not a religion that people convert to. It is a natural conclusion when people are presented with real history and scientific explanations of how the world works.
It does not stop you from engaging your parents in good insightful conversations though. You do not need to pretend being enthusiastic about Islam. Just be neutral with matters of Islam. Just discuss interesting discoveries in science or whatever else that you're interested in with your parents and why you think they are fascinating. Continue learning, watching documentaries, reading books and sites that are non religious.
I do hope that in time, your community allows for children like you to be free to explore what's true and not be stifled by religion.
Soon enough you will grow up, be able to support yourself and you will one day be free to admit that you're an Atheist to your parents. You can show that Atheists are not necessarily influenced by the devil etc or polluted by infidels. Rather they are the same people who just don't believe in the bullshit explanations of religion.
It's not long. It's only 5 to 10 years. Once you judge that it is safe for you to come out, you can and you should. For now, engage your parents to be more interested in other things apart from religion. Back away if it makes them angry or if it causes unfruitful arguments then try again later maybe with another approach to try and get a better reaction.