If I understand correctly, you basically have three EPG (guide) choices; if that’s the case, then unfortunately, what you’re experiencing is how Plex works by default currently. It will only allow you to choose one guide.
However, you may be able to work around this by creating an XMLTV file to use in place of Plex’s guide data.
You can search the forums or 'net for more info; here’s one example that mentions two possible sources for XMLTV data:
