Why does Wang Yuyan's mother hate the Mu Rongfu family?

You should know that Wang Jiahe's Murong family in Wang Yuyan is a pair of in-laws. But this pair of in-laws is equivalent to the enemy.

As soon as Mrs. Wang saw the Murong servants, she lost her temper and killed them as flower fertilizer. But in the play, Wang Yuyan asked Mrs. Wang many times, but there was no result, so Wang Yuyan came up with an explanation.

In Wang Yuyan's simple idea, the bad relationship between Mrs. Wang and the Murong family is mainly because Mrs. Wang is ruthless. Wang Yuyan's aunt, Mu Rongfu's mother, doesn't like Mrs. Wang. She thinks she is too vicious. She is a good second sai-jo, but she likes to kill people, which has aroused the resentment of Murong family.

But Wang Yuyan is still too simple. From the mouth of a mother beside Mrs. Wang, we can know that the relationship between Mrs. Wang and the Murong family is not good, mainly because of Mrs. Wang's infidelity. And he was born beside Wang Yuyan with an outsider, namely Duan.

So as a sister-in-law, how can I watch my brother being cuckolded, so I have a bad relationship with Mrs. Wang. And Mrs. Wang also hates Mr. Murong always mentioning the past, so it is natural to be rude to Mr. Murong.