Is Zheng Xiuren a friend of Eun Fei or Eun Xing?

I learned from my mother that Xiu Ren and Yin Sheng are friends.

But why is Yin Sheng so afraid of Soo-in?

And judging from the text message sent by Hideyoshi,

Yin Sheng and Xiu Ren should have a good relationship.