• betterchatmentions.disallow -- Excludes player or group from being mentioned by anyone
• betterchatmentions.exclude -- Allows player or group to mention everyone online
• betterchatmentions.everyone -- Allows player to mention everyone

Those last two seem redundant and do not honestly make a lot of sense.  What do I need as a permission to @everyone on the server?  Right now I hav all 3 permissions (since that's what the instructions say) and it does not work

Yeah, that's surely a typo in the documentation. It's been a while since I've visited this plugin so I'm not entirely sure the purpose of excluding. It was a request made some time ago.

I believe it's meant to circumvent disallows for specific players. I wouldn't use it if you don't need it. I'll revisit the code soon and figure out what 1 year ago me was doing.