Use a better relay device, that is stupidly expensive and completely the wrong idea for what you're trying to do. I2C is essentially for connecting between IC's on the same PCB, trying to do long distance is a crazy idea.
Here's an 8 relay board for very little money, and along with a cheap PIC you could easily do the job via a serial interface (RS232 type), you could even use a current loop if need be.
https://www.banggood.com/5V-8-Channel-Relay-Module-Board-For-Arduino-PIC-AVR-DSP-ARM-p-74110.html
Is there some reason you can't have the ESP near the relay board?, after all the whole point of the ESP is that it's wireless.