also: きょうだい
noun
older sister and younger brother
Refers specifically to a sibling pair consisting of an older sister and a younger brother. Not used for other sibling combinations.
彼らは姉弟で、姉は大学生、弟は高校生です。
They are an older sister and younger brother; the sister is a university student and the brother is a high school student.
姉弟で一緒に買い物に行った。
The older sister and younger brother went shopping together.
Gikun reading; the kanji 姉弟 is normally read してい. Reading it as きょうだい is a special, non-standard reading used in some contexts to emphasize the sibling relationship, but it is uncommon.
兄弟 is the general term for siblings (brothers) and can sometimes include sisters, but 姉弟 specifically means an older sister and younger brother pair.
姉妹 means sisters (older and younger), while 姉弟 is specifically an older sister and younger brother.
兄妹 means an older brother and younger sister, the reverse gender combination of 姉弟.
Compound of 姉 (older sister) and 弟 (younger brother). The reading してい is the standard on'yomi combination. The gikun reading きょうだい is a special reading applied to this kanji compound to convey the meaning of siblings, but it is not the standard reading.