Change your audio_init_2() function to this.
window.my_audio_2 = hypeDocument.getElementById("my_audio_narration_2");
//hypeDocument.getElementById("my_audio_narration_2").loop = true;
hypeDocument.getElementById("my_audio_narration_2").volume= .5;
window.my_audio_2.onended = function() {
hypeDocument.functions().show_hide_narration_2(hypeDocument, element, event)
};
This listens to when the Audio has ended using the Ended / onended event function
Have a read through this