You can have as many mics on the same channel as you wish, but you can only obtain independent control of the mics at the microphone itself under these circumstances. Most of the newer mics do not have interference problems from municipal and commercial areas, mainly because of the new FCC regulations that updated the frequencies a couple years ago. Most are not either 3G or 4G frequencies, and the range is very short, usually less than 100 feet at best.

You should not have any cancellation problems, despite the fact they are using the same frequency. However, if more than one person is singing or talking at the same time, this can produce some problems if the signal levels are not set identically.

Sounds like a can of worms to me,

Gary