Azula and Zuko only barely grew up together. If they ever got along they were too young to even remember, and most of their childhood was spent despising each other because their dad had a vested interest in ruining their relationship.
They were separated before they were either going through puberty, they next time they saw each other zukos voice dropped and azula had tits. Normal siblings that grow up together dont hate each other and also see each other go through puberty. Zuko and azulas case Is very specific and its not like many people in the world can even really relate to their relationship.