Fuji - I'm inclined to disagree - if someone is PIC, they're PIC. If I'm not happy they can do that job, I'm not there (nor are any kids or family I might have). Equally I'm not having anyone on board who thinks they have the right to intervene with the flight (advice I'm happy to take, at my discretion).
Fighting over the controls is not a healthy picture, nor likely to have a happy outcome.