Help! Weird light switch wiring in old condo

Hello!

I'm wrapping up a bathroom remodel, and came across a very weird wiring arrangement in the light switch, which I'm trying to replace/upgrade. Some background info:

There were two switches in the wall plate -- Switch A (left) controls both the light fixture in the room, as well as an overhead ventilation unit. Switch B (right) is and always has been useless. I had assumed it was unwired, but as you'll see below it's connected to something...

I had hoped to keep the light fixture on Switch A, and move the ventilation unit over to Switch B, such that they could be controlled independently. I'd still love to do this if possible.

Upon opening the wall plate, Here's what I've found:

Here's a picture, with Switch B removed for ease of visual inspection:

I've purchased a Legrand Adorne paddle switch and mounting plate (adorne® Decorative & Custom Wall Plate Designs | by Legrand | by Legrand) to replace this plate/switch, but it requires that the metal mounting plate be grounded. Given the weird wiring, I wasn't comfortable playing the guessing game trying to figure out what wires were doing what.

Any thoughts?

 

Which conduit is incoming and outgoing? Where does the conduit terminate?

The tan wire is your neutral, it is discolored.