Siblings; brothers and sisters — a collective term for brothers and sisters who share the same parents.
私には兄弟が二人います。
I have two siblings.
兄弟の人数によって部屋割りを決めた。
We decided the room assignments based on the number of siblings.
きょうだいは仲がいい家族が多いが、そうでない場合もある。
Many sibling groups get along well, but that's not always the case.
Brothers — sometimes used to refer specifically to male siblings (context-dependent).
彼は兄弟だけで育ったので、姉妹は一人もいない。
He was raised with only brothers, so he has no sisters.
その村には男兄弟が三人いる家が多い。
In that village there are many families with three brothers.
Siblings‑in‑law; brothers‑in‑law or sisters‑in‑law — referring to relatives by marriage in some contexts.
結婚してから、兄弟が増えて大家族のようになった。
After getting married, my siblings‑in‑law increased and it became like a large family.
彼は義兄弟と仲が良い。
He gets along well with his brothers‑in‑law.
Mate; buddy; comrade — an informal term used (especially among men) to refer to a close friend as if they were a brother.
彼とは学生時代からの兄弟だ。
He's a brother to me from my student days (we're like brothers).
チームメイトを『兄弟』と呼んで励ますことがある。
Sometimes teammates call each other 'brothers' to encourage one another.