At the moment whispers are all or nothing, there’s no way to have whispers siloed in a way that one group can only see certain whispers. The best way to discuss something within a specific group is to send a message to the group or create a category only they can access.
As a feature group-specific whispers could get complicated pretty quick… we’d need to come up with ways for people posting whispers to decide which group can see the whisper they’re about to post… and a way to communicate to readers who can see a specific whisper. Certainly not impossible, but I’m not sure it’s the kind of complexity we’d want to introduce.