Android Question Phone voice message

It is hard to give you concrete advise, cause your post isn't very concrete...

For 1) i think you should start to search the forum for text-to-speech (or TTS). Get to know about it and start a simple app which reads a predifined sentence to you on button click. When this works make it more complex.

For 2) i would use a different approach: send a text to someone via FCM and when the other person recieves it use TTS again to make the app read the text.
Don't know if it is possible to send recordings within a phonecall....