Two flyers on the same frquency at the same location is always a bad idea. Sooner or later due to capture ratio, one flyer will step on the other and at least one (if not both) plane will meet an early fate. There are systems with the transmitter ID recoginition and so on, but the power of one transmitter in too close of proximity to the other guys receiver will eventually make it fail.

Even if you can get lucky and get away with this, in the US the AMA will not allow it.

Good luck.