The story is a bit all over the place now.
I only understand that Seungju absorbed Muheun's spiritual energy. But not others??? So if there's someone else spiritual energy he is absorbing will be tied back to Muheun. Personally for me I want to know how his siblings died and are they closed to Muheun and his sister since the age gap here is big. The way it was being casually throw here that Seugju's siblings died while he's the only lasting members of the children is out of place too. I am saying this because in the synopsis it is a pretty heavy point and a running curse in the family. So it makes little sense that the story is not develop properly around it.
Anyway, looking forward for more chapters and hopefully a few things will be cleared up as well.
You mean to say both his brother and sister died?? Like the way the character said his sister died is so detached.