I'm a bit confused about Sihan's past. How come both his parents are human/servants and he...

He was turned by Ryan, if I'm not wrong

http://www.mangago.zone/read-manga/royal_servant/uu/royal_servant-chapter-20/
http://www.mangago.zone/read-manga/royal_servant/uu/royal_servant-chapter-22/1/

His mother (presumably) was killed by his father via a liquor bottle, and then his father sold him off to a slave market when funds were diminishing; When Sihan encountered Ryan, he requested that Ryan turn him into a royal blood. Ryan gave Sihan some of his powers to induce a mutation in Sihan, from a servant to a royal blood, without the need for a core. Sihan survived the painful mutation, didn’t die from it and developed a core, completing his transformation into a royal blood~

Ryan put a core in him when hi was a child because Sihan asked to be more stronger
y no se por que lo puse en ingles cuando sale una bandera chilena en tu user xD

Buajajajjaajajajajaj después de leer toda tu respuesta me doy cuenta recién que la persona que publicó el post es de Chile viva Chile!

Thanks a lot!

jajajajajjajaj siii