multicam with overlaid audio

I have two cameras and a mic. I want to do multicam in DaVinci 18 but with the audio from 1 camera and the mic overlaid, as they are when I play things in the timeline. But I only seem to be able to select 1 audio track at a time. I need two. How do I do this?

A simple way is to copy the audio from each clip and paste under the multicam audio. Then disable the multicam audio track and mix these two extra tracks of audio as needed. You can do this from the multicam clip. Right click on the audio and select one, then render the audio as wav, change and do the other one. They will then be in sync on the combined timeline.

I know how to switch between the tracks, but I want both at once. One is near the chorus, and one is from the auditorium to get the orchestra. I have synced the audios and videos.

I don't think you understood what I wrote. Make copies of the audio then when you edit in multicam mute the multicam audio track. The extra audio tracks will not be affected by cuts etc but will always be extra audio tracks under the multicam clip in the timeline. You can then mix either in the edit page or Fairlight page independent of the multicam edit.