You know I felt the same thing except the fact that I was better and I was bullied by them. I even talked about it with my parentsbut didn't work for me. I felt very sad and raged but I couldn't help myself. All I did was accept it. I made peace with it. I ignore now. When it bothers me very much, when I feel unheard and misunderstood I write it down in my notepad. But I'll advice you to sit with your parents with a cool mind and talk how you feel about it. Communicate what you want. Calmly tell your sister how her behaviour makes you feel miserable. If she's good at public speaking then I'm sure there's something at which you are wonderful. Explore that. You arent any failure. You are trying and that's what matters. Better yourself. Make yourself so engrossed in your own betterment that you forget all this. I hope this helps :)

I can understand how you feel. Since she is your sister, you cannot avoid her as you're both bound by blood. What you can do is, try to talk to her and make her understand how she has been undermining you. I understand that you've already tried talking to your parents, but you can collect proofs of her behaviour by recording it and show it to your parents. Don't spread it and put your sister to shame by doing this, but you can make your parents understand what you've been going through. Secondly, you can maintain a distance from her. Talk less, ignore her actions, do your thing

Have you tried talking to her once about you want to change the dynamics of your relationship with her. And you would like to strengthen the bond.

Yes I have tried. Not once but many times. She even slapped me once. Every time I try to explain her that her words are hurtful, she in return lecture me that it's me who's taking things in a negative and serious way

Maintain a distance from her. Preserve your peace.