API to send messages to groups of players?

Is there an API that can let you sort players into certain groups and then when they text chat in the main chat, only let them see other members of that group? When I run social scenes like all the PCs in a tavern, they will often split up and talk to multiple NPCs separately -- this makes it very cluttered and hard to track what's going on. If there was a way to only show what they should be seeing or hearing it would be good.

You can use the Language trick. Assign control over a character called "Group A" (or whatever) to all the players in Group A. Whisper to "Group A". All Group A Controllers can see the whisper, and if they post as "Group A" only Group A controllers and the GM can see it. They may have to identify themselves as they speak. but it should work.

The problem is that if you have a lot of players moving around (like moving from one NPC to another after a convo ends) then it requires a ton of micromanaging by the GM, constantly changing who owns what, and I foresee it will be easy to forget in the middle of juggling all other GMing activities, or accidentally leave someone out. That is why I was wondering if there's some API possibility to affect the chat itself. Also I don't think that the chat log stores whispers.

True, it would be difficult to manage, but could be made less so with a judiciously crafted token-mod menu. I'm not certain of the current state of the chat log rules. I don't use it very often.

The chat log does store whispers, if the person viewing the log is someone who could have seen the whispers in-game to begin with.

Oh, so it doesn't get rid of them or only store ones sent to the GM? For some reason I heard that it did that.

No to both of those.