Responses
This dynamic is a direct result of their distinctive family structure. While Yuri is indeed his brother, his role is more akin to a servant to Yonhee, who is the chosen vessel of the family's deity. It is a long-standing family tradition for members to serve the chosen vessel, and Yuri was personally selected by Yonhee for this specific duty.
Only up to chapter 31, could someone I guess spoil me - I don't understand the animosity towards Yuri? And why does he allow Yonhee to treat him like that?m
It's also been a while since I read In the eyes of Sora so maybe there's context there. I'm just impatient, idm spoilers lol.