Final Cut Pro X multiple audio channels auto muting
To my knowledge, there is no feature or even a plugin what can monitor one audio channel and adjust another. I would see that as it is the job of the editor or sound engineer. That's the reason you get paid the big bucks I guess. 

Better microphones definitely can help. If you get microphones which have a very distinct range you can limit the echo effect. You might consider asking in sound engineer group what microphone would be best for your situation.