I know all too well that sometimes siblings are treated differently for a good reason. It can sound cruel to give privileges to one of your children but not another, but when one kid has constantly abused privileges and cannot handle any level of responsibility, it's no wonder that they'd be treated differently than a kid who has proven they can hang. That doesn't necessarily mean that one kid is favored over the other. It just means that they've earned trust while their sibling hasn't.
One younger sister recently went viral on Reddit after she was accused of being "the golden child" by her dropout sister. She was sick of being labeled as such because the only reason she was favored was because she always getting in trouble. Subsequently, her older sister called her a jerk and fled to her room. While the majority of Reddit sided with the so-called "golden child," one poster was skeptical of her side of the story.