I'm not sure if you know this or not but your supposed to be Tiffany's sister and not just her sister but her TWIN. Are you aware that your sister is in the hospital because you decided to push her? Not only is her arm broken, her knee scraped, and her ankle twisted but her heart is also torn. If you had pushed her all the way down the stairs like you wanted to your sister would have been the second friend I lost to death.
My first friend was this girl named Ashanti. I still remember the day she said casually "my blood is sick". She had Leukemia which quite literally means cancer of the blood. Over the months I read many articles and stories about kids who survived Leukemia but not my Shanti. How could you willingly almost let your sister die?
At one point in time you guys were best friends. That was before I met Tiffany though so I'm not sure of why you guys aren't friends. Is it because you guys let Kelsey eat a hole into your relationship? I've talked to Kelsey and me and her are far from friends but did you know that her parents are divorced and it hurts her to see happy families?
You might not be able to fix your relationship with your sister but you need to try. Did you know there are two types of hate the kind within a family and the kind between to two individuals or groups of people? I personally think both are as strong as each other and need to be eliminated. Plus if there is hate in homes there will be hate in the world.
P.S- Sometimes small steps fix relationships, not big leaps.