Sibling rivalry is really a competition for the love and approval of primary caregivers. The reason this need for love and approval takes on epic dimensions, causing strife, is that in the mind of children parents are godlike figures and their family environments are the world. Primary narcissism is something we all deal with to one extent or another. It’s that secret belief that we’re the center of the universe and everything revolves around us. The maturation process is about expanding those intellectual and emotional boundaries to become more objective in how we see the world.
One way you can help yourself on that journey to objectivity if you still feel a sense of competition towards your siblings is to realize how arbitrary it is to compare yourself against those specific people as opposed to comparing yourself against anyone else. Just because they happened to be born into your family of origin shouldn’t factor into the equation. The group of people who make up your family are not representative of the world, they’re just a few people who live in it and ended up spending a lot of time together due to how we structure family environments in the West. Your parents aren’t gods, they’re human beings with their own flawed opinions and frailties, probably doing the best they can but certainly not the final judgment on anything.
A competitive spirit is never going to make you happy and it takes energy away from where it needs to be going, which is actualizing your own unique potentialities. Who cares what your siblings’ traits and talents are? Let them have these things and work on developing your own. The more time you spend on yourself the less time you’ll spend worrying about anyone else.