Massive spoilers from the raws regarding the plant
The "original target" was Moryeon, the reason he was fine after drinking the tea is because the plant is only poisonous to Alphas! Look back to chapter 6 the 1st brother was staring at Moryeon drinking the tea and he refused to drink his cuz he's also suspicious of how this happened. Yeju knows about this plant due to the modern world
He goes back to the fourth brother Seobun and lies that he doesn't know about the plant to protect Moryeon's secret as everyone will find out he's an omega if they knew. Seobun was really upset but he still gave him back his stuff cuz he didn't care anymore it seems he really loves his brother that died
Massive spoilers from the raws regarding the plant
The "original target" was Moryeon, the reason he was fine after drinking the tea is because the plant is only poisonous to Alphas! Look back to chapter 6 the 1st brother was staring at Moryeon drinking the tea and he refused to drink his cuz he's also suspicious of how this happened. Yeju knows about this plant due to the modern world
He goes back to the fourth brother Seobun and lies that he doesn't know about the plant to protect Moryeon's secret as everyone will find out he's an omega if they knew. Seobun was really upset but he still gave him back his stuff cuz he didn't care anymore it seems he really loves his brother that died