As much as I don't like when groups translate all the terms like "onii-chan" or "oji-san" or whatever, settling with just "brother" rather than the cringeworthy "big bro" seems to be a decent compromise
"i wanna make this romance series with a girl that loves her brother"
"naw you cant bro thats degenerate"
"alright then it's gonna be her friend instead"
"wow thats genius bro how did you do that"
@BCS brother would sound like what people at church call each other. Honorifics dont exist in western culture so you cant really understand the way theyre talking unless they leave it as is. There's onii-chan, onii-san, onii-sama, onii-tan, nii-san, aniki, etc, and only one brother word in the english language. I'll take accuracy over localizations that miss the meaning.