Even if you haven't or aren't a professional audio engineer for your podcast, you can at least make your volume levels better:
use ffmpeg's EBU R128 meter and loudness normalisation filters to understand why some are very loud and others are like whispers.
Meter: https://ffmpeg.org/ffmpeg-filters.html#ebur128-1
Normaliser: https://ffmpeg.org/ffmpeg-filters.html#loudnorm