Can I switch my bathroom light and fan separately with two conductors?
Yes, but you'll need smart devices to do it

In the smart-switch wiring, you also have a controller module up in the fan assemblt.   The smart switch and controller both get always-hot and neutral.   The controller then outputs switched-hot-fan and switched-hot-light. 

The smart switch and controller must be a matched set.  You probably won't need a 2-gang box for the smart switch.