Generally now there is a meatloaf number two, because the standard UART is not a multidrop network, so in fact you should only directly connect 2 devices via UART or use a transceiver e.g. RS485, which makes it possible to connect more receivers to the communication lines. Or use two UARTs in one esp (if there is such an option there, because I don't know how many are derived), then you know with whom and what you are talking about, well and you have a point-to-point connection, not a multidrop. If you were using something like RS485, though, you could enter the address of the controllers and then you send the ID and the variable, and then you're able to recognise what the data is and from whom. Because just the bytes of the variable in the buffer won't tell you, and you can put those bytes into anything and the "system" won't stammer...
And what topology do you have? The 3 esp are at what distance from each other? Because maybe you only need one that handles all the slaves over I2C and the whole thing is overkill? Because you probably have enough resources in a single esp.
Added after 2 [minutes]:
PS. if you have some longer distances, then pulling a bare UART out into the world is not a very good idea. And if short, you don't need 3 esp
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And what topology do you have? The 3 esp are at what distance from each other? Because maybe you only need one that handles all the slaves over I2C and the whole thing is overkill? Because you probably have enough resources in a single esp.
Added after 2 [minutes]:
PS. if you have some longer distances, then pulling a bare UART out into the world is not a very good idea. And if short, you don't need 3 esp
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