i don't think so
They are brothers and im pretty sure they are related because they have the same green eyes (its a more obvious green in the early chapters).
Half brothers I think
I don’t think they’re full brothers if that’s the case cause myeong-li only told Jingi about his mother passing, if they were brothers myeong would’ve told them both
I thought they had the same dad and different mums but maybe I just imagined reading that and it wasn't explicitly said
Oh yeah are the grey haired guy and brown haired guy brothers?? I remember hearing something about it a while ago, I mean I know that they aren’t full brothers cause one’s myeong-il only told one. I hope they aren’t related at all