Recent renovations have left a room with light switches in slightly undesirable places.  Essentially, an existing room with a switch at one entrance needs an extra switch at the other entrance in a setup as if it were a hallway.  Running additional cables is not easy.  I have an existing HASS based automation system, but I want to avoid relying on it entirely for something as critical as light switches.

Here is what I am thinking, but I'm pretty new to this and would love to get some confirmation that it will work.  

• At the existing switch location, install a Shelly Relay (mini Gen3).  This will function in edge mode and directly control the power circuit to the bulb.  If the power is on, this switch must toggle the bulb when switch toggled.
• At the new switch location, a second Shelly Relay.  This relay has nothing connected to the output, it is just sampling switch state.  If this switch stops working it is not the end of the world
• Home Assistant will monitor the second relay, when that relay changes state (ie, switch flipped), the first relay will have its output toggled.
  

   

  • I understand the Shelly's are somewhat programable.  If it's possible to remove HASS from the control loop entirely, that would be ideal.

This video is very close to my thoughts, but is using a third relay and requires HASS - https://youtu.be/EliCUBtSWJ4?t=442

I had a surprisingly hard time finding any information out there that matches the setup that I think will work for me.

Cheers!
Brad