noun, noun which may take the genitive case particle 'no'
among friends; within one's circle
Refers to something happening or being shared only within a close group of friends or acquaintances, often implying exclusivity or informality.
その話は仲間内だけの秘密だ。
That story is a secret just among us friends.
仲間内で集まって飲み会を開いた。
We got together with our close circle and had a drinking party.
内輪 also means 'private' or 'within a group', but can be used more broadly for any in-group, not necessarily friends.
Compound of 仲間 (nakama, 'friend, companion') and 内 (uchi, 'inside, within'). The reading うち for 内 is the native Japanese reading.