My second sister's husband (SIL no 2) and my mother had been very close since day one. They were so close that SIL told my mother as long as she help take care of his son she will be well taken care by him and if she ever get sick he will pay for all her medical fees when she grow old.

My mother has been staying with them for like 10 plus years with my second sister and SIL. There has been no issues and my sister's oldest son is very close to my mother. But my mother and sister has not been getting along too well.Few years ago my sister was angry with my mother over issues with the way my mother bring up her son, she asked my mother to move out and they did not speak for months.

My mother eventually moved into my brother's house and stayed for two years to help him take care of his son. During that time SIL tried to persuade my mother to move back when my sister is ready but my mother refused as she do not want to get into another despute with raising children. She continue to stay at my brother's house. Due to this reason SIL started to be unhappy with my mother and jealous of my brother.

Not only SIL started to stop greeting my mother when she drop by visit sister's son, he also complains to his family members that my mother did not respect their earlier agreement that she should stay on to take care of his son. To him, my mother prefers to take care of own grandson and ignore his son. This complain eventually went to my mother and she was unhappy with SIL ever since.

This misunderstanding goes on for years. Till now my mother and SIL has not been on talking terms. Though now SIL greet my mother but both are not happy with one another.

Basically SIL will be treat MIL well for two main reasons: (1) To make wife happy (2) Need MIL help to raise his children