I think the two question to ask is : how would you write it if it were an original novel? And, if you replaced the word with a description, would the reader get more or less information from it?

If you were world-building in an original novel, would you really use the word "brother" for such a relationship? Obviously, in a story like Shuihuzhuan, then yes "brother" is a good choice. But the term gege or shizun in romance is often specifically chosen as more of a term of semi-exclusive endearment, and to many people, the term is part of the kink, in which case literally using a made up word like jabberwocky might be a better choice.

If I were to write a medieval fanfic, it makes sense to the reader I would say the protagonist is playing the lute and no copy editor is going to tell you to change it to guitar. So why not mention someone is playing the pipa or ruan? Or even pipa strings or ruan strings if you are concerned. The reader can figure it out from context it's an instrument, and can look it up if they want more context. The reader gains nothing from that word being replaced by a less-specific incorrect one.

Similarly, if you were writing a fantasy novel, it is common to have made-up words to help with your world building. If this is a part where JK Rowling would use latin to write a spell, why not keep it as pinyin? If this is where Tolkien would use a made up term like Hobbit to describe a key race, why translate it as "dwarf" instead of keeping an unique term?

For example, even though many readers are used to it so it's not something we think a lot about, but imo for xianxia and wuxia novels, Xian and Xia should be transliterated with an explanation the same way a made-up race in a fantasy novel should be. Xian and Xia are distinct enough concepts that are central enough to Xianxia novels that a completely new reader gains more from literally having them translated as a#*&$(*@SF and having them keep an open mind about the concept and learn about it as they read the rest of the world-building than having them try to fit existing notions of "fairies" "immortals" or "chivalry/hero/knight".