Here is where you can get the list of chatters:
https://tmi.twitch.tv/group/user/:channel_name/chatters
Where :channel_name is the login name of a channel. This is the same endpoint that Twitch uses to show the list of users. It’s not very reliable and may take multiple requests to get actual information. If you want to connect to chat, then here’s the guide to Twitch’s IRC: https://dev.twitch.tv/docs/v5/guides/irc/ – there’s a ton of libraries available for tons of languages.