For translators/proofreaders:
Please leave the words as "nee/onee/nii/onii -san/chan" or whatever it is correct in the Japanese language. English does not have words that younger siblings use when they are referring to an older sibling. Translating them as "big sister" or "big brother" is wrong as it doesn't flow well when spoken in English. Either they need to use their names or use the shorten forms of the word.
Example on Page 16: "Big Sister, your face is red. Do you have a fever?" Instead you should use any of these ⬇️
"Sis, your face is red. Do you have a fever?"
"[Name], your face is red. Do you have a fever?"
"Onee-chan/san, your face is red. Do you have a fever?"
"Nee-chan/san, your face is red. Do you have a fever?"