I don't think they will ever do. Pronunciation would probably be the same as modern Greek considering that no valid ancient pronunciation arrived in our days (i.e. no recordings are available). Phonetic studies and books are also available in the last 300 years so in my opinion shouldn't be considered valid for a language continuously spoken and evolved 2000+ years before. About the grammar there are many books that you can find and study.
Tú habías pensado que era zeta, no theta, ya que estás tratando de traducir tus clases de griego al inglés donde zeta ζ se pronuncia theeta aunque la pronunciación real en griego se acerca más a la pronunciación española. Pd. Soy mexicano, pero lo comprendí perfectamente.
Hello! Please read the Tips and notes that are available on the website, just scroll under the lessons. You can also find information on how to add a Greek keyboard here and here. Basically, you need to activate the Greek keyboard by accessing your computer or mobile device language input settings.
Thank you for clarifying. In the future you can report audio issues through the REPORT button as soon as you encounter them. Unfortunately the ABC unit audio is problematic so I suggest complementing your learning with other resources (which will help throughout the course in any case). Forvo.com is good for audio in general and you can also check out the resources posts in the Greek forum https://forum.duolingo.com/topic/936. Just learn the alphabet and get out of the first unit, the rest of the course is much more fun! Happy learning!