What if my brother bullies my sister?

1 First of all, from the perspective of my brother, understand why my brother bullied my sister and understand the whole story.

Secondly, if my brother is wrong, I will criticize him and establish the idea of protecting my sister.

If your sister is wrong, you shouldn't be partial to her just because she is young. Ask your sister to apologize to your brother and encourage your brother to tolerate her.