People who are peers or in the same group; friends, colleagues, or comrades among themselves.
仲間同士で助け合うことが大切だ。
It's important for peers to help one another.
仲間同士の会話はリラックスした雰囲気になる。
Conversations among friends tend to be relaxed.
部活動では仲間同士の協力が勝敗を左右する。
In club activities, cooperation among teammates determines victory or defeat.