
My technique is to not use the Multicam audio at all.
1. When creating a Multicam, only add camera clips. Don't add separately recorded sound.
2. After adding the Multicam to your main timeline, add any audio you actually want to use under the Multicam and sync it up. This includes separately recorded sound as well as camera audio.
3. Disable the audio from the Multicam.
Keeping the usable audio out of the Multicam makes mixing the audio in Fairlight much easier.