XF 2.3 Limit member list user by user group membership (travel/event forum use case)

[stevenfreiburg]

Hi everyone,

I'm running a XenForo forum used by several travel and event groups. Each group should only see and contact its own members — but not members of other groups or the forum at large.
So far, XenForo seems to allow only “everyone sees everyone” or “no one sees anyone”
for the member list and “Who’s Online”.

Goal:
Show the member list and online users
only for users within the same user group(s)
without creating separate forums or disabling these features globally.

Is there any add-on, extension, or customization that can make member list visibility depend
on user group membership?

Thanks for any advice or examples!