What does my brother call my mother-in-law

Auntie. Brothers and sisters of a woman's family should be called aunts or aunts when they call their sisters and mothers-in-law. Although different regions have different names, they all mean this. It is ok for a younger brother to call his mother-in-law after his sister, and it is better to call him aunt. Even if it doesn't matter at all, a stranger can call her mother-in-law.