Okay, I think I understand what you want to achieve, and it’s the same as what I imagined when I first read your post. The thing that confused me was wanting to have the MCU on one gate control the others - that’s not the best way to go.
Each MCU should be created in Blynk as a separate device, with its own Auth code, but all linked to the same project This way, the Online status indicator in your project will show the on/offline status for each device.
When you set-up the buttons in your app, choose the correct device for each button.
Each MCU will connect to a relay, and that relay will be controlled by making a pin go High or Low, depending on the type of relay you use.
I use the Wemos D1 Mini and the Wemos relay ‘shield’. these can stack one on top of the other or sit side by side on a doubler/tripler base.
My setup controls just one gate, but I also have an RFID reader attached to it, so that I can open the gate with an RFID tag, or the Blynk app (or a 433MHz button to release the gates when visitors arrive).
I trigger the electronic lock release for 5 seconds once the signal from Blynk/RFID/433Mhz is received.
My gate release is a 12v AC device and I found that I had to put a 220uf capacitor across the relay terminals to prevent interference with the MCU.
This thread shows a shot of the MCU, Relay and PSU/level shifter needed interface with the RFID reader, on a Wemos triple base, but the 220uf capacitor isn’t shown here::
Please dont ask me for my code, as I use Blyunk in a very different way to most people and it wont work in your infrastructure unless you have a Raspeberry Pi acting as an MQTT and Nod-Red server.