Stuff so the story makes sense

Ling Feiji is the 13th princess and 16 years old

Her father is the emporer of Jiu Bei

Her mother is the second wife of the emporer

Her eldest sister is married to a prince of the neighboring kindom

Her two second eldest sisters are twins and always take each other's side

Her second and third youngest sisters are strong political figures and one is married

Her fourth sister is a military secretary

And the rest of her sisters are in the spy business like Ling Feiji

Liu Shanbi is the 5th prince and 20 years old

His father is the emporer of Xin Liu

His mother is the one and only wife of the emporer

His eldest brother is in line for the throne and unmarried

His second and third eldest brothers are married

His fourth brother is the head spy master

His sixth brother is sickly and ill since birth