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If you feed multiple transmitters via the Internet, you’ll going to get random delays and you won’t be audio synched.
One alternative to the internet is some sort of proprietary wireless feed, such as that used in Trango and other equipment (which does not require a license). With the proper directional antennas, you can get ranges that would meet the requirements here. You would then have to synch the audio of the various multiple Part 15 transmitters.
Again, I’d recommend searching this site for the various discussions on synching multiple transmitters – it can be done, but there are a lot of considerations.