
I'm confused about the beginning of the story. Who is who??????????

You mean the character Kwon Minjae. He came from the main story entitled "Still, I like it". He is paired with Seo Jinwoo aka Damon's younger brother Seo Hyeonwoo. He is also the first love of Damon.
This is a spinoff for Damon to have a happy ending. Since the Kwon Minjae in the main story is a total coward and a shitty bastard who used Damon because of his talent and also because Minjae fell in love with the younger brother then he left him when he realized his mistake then played a victim everytime Damon wanted to meet with him.

I'm mad at every one except the Achilles family, the mc, the high priest, and the count amd countess that treated the mc like their daughter. The rest could just go poof!

They are just writen to be easy to hate and dumb, really, really dumb. Their action, thoughts and decision making prosess are outside the norm. I mean, it is possible for a couple people to be unreasonable and/or malicious but in this book only a handful of characters are portrayed as "good". That is like the whole world is filled with malicious dummies and only the Achiles and counts' familiea are sane.
Grab ye torches and pitchforks! We are burning the Duke and the Duchess! ヽ(`Д´)ノ