This is always a problem when working with amateurs. It makes editing a lengthy and painful process. The real solution is “don’t work with amateurs unless they are willing to learn”. Failing that, ensure that everything is recorded at a low enough volume to avoid clipping, and expect to do a lot of editing. Unfortunately there is no magic bullet.
Plug-ins such as “LevelSpeech2.NY” (Improved "leveling" for speech - #27 by Trebor) and “AGC” (AGC - Automatic Gain Control) can help in some cases.
Note that Windows often provides automatic gain control in the “Sound Enhancements”. We generally recommend turning that off as AGC is killer of high quality recording.
Another alternative is to record with a portable recorder. There are many models available, and they frequently have features like AGC and voice activation. As with computer recording, for high quality recording, it is usually best to switch those features off and use manual editing and compressors in post production.