Sibling dynamics can change a lot over time. My sister and I were much more adversarial than super friendly when we were kids. It's not like we hated each other, but we would fight, she would bite, and looking back, our conflicts seem a bit trite.
Some siblings cannot overcome their childhood rivalries and never become friends. It would be kind of silly to still be mad at your sister for borrowing her clothes without permission during her sophomore year of high school. However, holding a grudge can be downright necessary if she was consistently and unusually cruel to you for years without so much as an apology. That's the situation for one little brother of 2 incredibly close sisters. They spent their whole childhood excluding and rejecting him, and now that they're adults, that behavior hasn't changed until recently. Now that they need him, they're trying to get him back into their lives.
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