Mato's translation comparison doesn't cover this line, so I can't easily link to the full context, but this is a young girl (Rydia) scolding an older man (Edward/Gilbert) for being too overcome with grief to take action. In the original US translation, the dialogue is "Crybaby! You are a man! You are a grown-up! You are not the only one who has lost loved ones!" The more literal translation would be "Aren't you a man?" but the meaning is the same.

"Brother" seems to be coming into it because Rydia is addressing Edward as "o-nii-chan". Pretty classic example of something that you couldn't translate accurately without knowing who the characters are.

"o-nii-chan" is a great example of translation difficulty because it's very natural in Japanese to refer to your older brother as "o-nii-chan" and it sounds like bad exposition writing in English.

And in this case it's just being used to address an older but not elderly man, in a way that's totally normal in Japanese but would be utterly bizarre in English.