This is about translation. If you're a translator, you should consider nuances like slang and how people actually use certain words. Hyung doesnโt just mean "brother" it also signifies respect for older male friends or people someone values. In this case, they are clearly not brothers, as anyone can see. Using "brother" in the translation creates confusion for people unfamiliar with the term, leading them to assume it refers to blood relations. A better alternative could be using "senior" or even the characters' names to avoid misunderstanding.
You could also simply keep the word hyung. Most people are familiar with the term by now, and if not, a translator could add a small note explaining its meaning. As a translator, itโs your responsibility to ensure readers can fully understand the context and avoid conflicts or confusion. A careless translation like this can ruin the entire tone or meaning of a panel.
Brother fits enough. It doesnโt necessarily mean that you were born of the same parents. In casual talk you can see people calling their closest people their brother/sister, its the same thing! I do think hyung would help new readers who are confused, as koreaโs use of โhyungโ is more common and ingrained in their culture. But I believe most people would understand context, and the meaning of brother in this occasion!
I hate how they use the word "brother" instead of hyung like bro