Why did my sister-in-law ask her brother for money, and he immediately gave it to her? And my sister asks her brother for pocket money, but he always doesn't give it?

In fact, it is obvious that after marriage, a man and his wife are a whole, that is, a small family, which is different from unmarried. They should be responsible for their small family. Unmarried and their sister's parents are a whole and can be casual. Therefore, it is correct for a sister to understand her brother's behavior and to respect and understand each other.