I have 2 sisters. One just turned 18 and one is 13. In regards to the older one, well... in actuality, we are absolutely nothing alike. She is so in love with herself that she would make Narcissus look humble, whereas I hate myself to such an intense degree that I nearly flunked out of college due to spiraling depression. She is a consummate liar, drug-using, extrovert, whereas I am bluntly honest, devoid of any "fun" (in the social sense), and incredibly introverted. She is an atheist who believes in every conspiracy theory and paranormal piece of bullshit that she comes across, whereas I am a christian who, despite my religious beliefs, holds science and rationality as incredibly important. Also worth noting, is that belief in the nuttier conspiracy theories is the only thing I mock incessantly. A lot of these differences is due to the fact that we both have been diagnosed with Bipolar disorder, with me being primarily depressive and her being primarily manic. It runs in our family and I find it a bit funny how our vast differences in personality have the same underlying causes.
My younger sister is a lot more difficult to compare though. Frankly, we look nothing alike and I think we may not even have the same dad (my mom was not mentally sound and cheated on my dad a lot) but personality-wise she is somewhere in between me and her sister. We definitely have the same interest; we like the same kinds of movies, a music, and hell I even got her in anime (where she went hardcore otaku). She even acted like me up until recently, but then decided to take on other sister's worse traits: the complete disrespect for everyone who isn't her, the need to get the last word on every issue, and the stubbornness of a brick wall.