I’ve got a friend who’s an electrician that can help me but doesn’t know home assistant. Any advice in what hardware I need to make this work?
You’re right, playing with electronics beyond my knowledge is clearly not working out. For now I’m leaving the Shelly’s to the wall switches 
He doesn’t need to know Home Assistant. I would look at the Sonoff 4CH with ESPHome flashed to it. You can use the EWElink firmware that it comes with, but you wanted to integrate it with Home Assistant. I would put the Sonoff device near or in the device in post 7. I suspect that this is where the wires for the switch originate. And remove or disconnect the switch and connect the wires originally going to the switch to two relays on the Sonoff. You can control the fan with Home Assistant, but make sure your programming prevents both relays from going on at the same time.
There is rumored to be a way to flash ESPHome through the EWE update, but I’ve always soldered header pins to the board and use a UART.
I’m familiar with esphome and soldering so that should be going better then this 
thank you for your advice!
My mistake was seeing a white and two black wires from the switch and assuming the white was the common from the switch. On closer inspection it is a white/brown wire? Maybe if you had started with photo of the starting point I would have realized that the left connection box was the switch and not wires from the switch. In the future, turn off all power to the devices and use an ohmmeter to map where all of the wires go and how they are connected. From that information you can draw a schematic and the solution is instantly obvious.