The fact is that you outshine our sister in many ways, so she feels insecure and inferior to you... It's a kind of compulsive projection because they can't face the truth that in the way they assess people, you surpass her. I'm very familiar with this dynamic as I have four sisters who struggled academically while I did not, and they just can't bear it !!!I don't care about what grades they got/and such like, but they can't let it go! There resentment is like a cancer in their soul, eating away at them. The best we can do is keep our distance and not take it personally.