親子, 兄弟 and 姉妹: parents, children and siblings
Compare a parent and child baking, ducks walking by a river, siblings sharing a room, and sisters performing together. Keep the relationship direction and sibling range with each Japanese word.
親子 connects a parent with offspring
親子 (おやこ) identifies a parent-child relationship. In “休日に親子でクッキーを焼いた。” (“A parent and child baked cookies together on their day off.”), a parent and child baked cookies together on their day off. The sentence names that relationship rather than participation by every family member.
In “川辺を鴨の親子が並んで歩いている。” (“A family of ducks walks in a line along the river.”), the ducks walking along the river are described as 親子. The relationship can include an animal parent and offspring, and the word itself does not establish a total of exactly two ducks.
兄弟 includes siblings in these examples
兄弟 (きょうだい) identifies siblings. In “兄弟で一つの部屋を使っている。” (“The siblings share one room.”), the siblings share one room. The number one counts the room; it does not tell us how many siblings share it.
In “私たち三人兄弟は性格がそれぞれ違う。” (“The three of us siblings all have different personalities.”), 三人兄弟 identifies three siblings with different personalities. Keep the translation's sibling range rather than narrowing this example to an all-male group.
姉妹 identifies sisters
姉妹 (しまい) means sisters. In “あの姉妹は同じ楽団で演奏している。” (“Those sisters perform in the same orchestra.”), those sisters perform in the same orchestra. The shared orchestra is part of the scene in which their relationship is described.
In “姉妹で色違いの帽子を選んだ。” (“The sisters chose hats that differed only in color.”), the sisters chose hats that differed only in color. 親子 supplies a parent-child relationship, 兄弟 a sibling relationship, and 姉妹 a relationship between sisters; avoid supplying an unstated headcount from the relationship word alone.
Must 私たち三人兄弟 identify three male siblings?
Show the answer and why
No. This example identifies three siblings whose personalities differ. Preserve that sibling range in 兄弟 while distinguishing it from 姉妹, which identifies sisters.