Audio Clean Up

I have 3 audio files which were recorded on a zoom mic to pick up multi-directional voices during a training role play session.

The result is low volume with a background hum. I'm not sure if the hum is from the room or a poor quality zoom recording. I tend to think the latter.

I have tried to remove the hum but it is not satisfactory. Starts to sound very robotic. Could you take a look at the attached sample file and let me know if you can tidy up by removing the hum and increasing volume. Plus, if possible, less treble and more bass.