That's not Byul's job, he is their kid, he doesn't have to be considerate especially when he is only stating the truth. What Hyesung went through was terrible and he should have all the support he needs, but Byul shouldn't be one of that, even more knowing that Byul must have his own insecurities and difficulties regarding his birth (even if he thinks otherwise)...
Shut up, he is his own person, not an extension of his mum, he feels sorry for a lonely old person who did nothing to him, plus she is his grandma. And Hyesung should control his temperament since he is not the teenager in the house. I will not feel sorry for a 30 something year old screaming at a kid.

Everyone is wrong here except Byul, don't raise your voice on him (╬ ̄皿 ̄)