The brother-in-law understood his sister-in-law's feelings

My wife will give birth next week at a hospital in the city. So my husband and I went to stay at my brother and sister-in-law's house to wait for my wife to give birth and then go to the hospital for convenience. A few days at my sister-in-law's house, I realized that her family was not happy because my brother was physically weak, which made my sister-in-law quite disappointed. I saw that and decided to help her and thought it was right. But I didn't expect that my sister-in-law would go against “good intentions” mine.