You cannot have an isolation if your power ground and your digital ground are the same.
In case you want an isolation, you can use any isolation amplifier like the ISO130 between your resistive attenuator and the analog pin of your controller.
For total isolation between the power ground and the controller's ground, you must ensure that you have an auxilliary supply to drive the input(Power Side) and another one to power up the output (Controller side) of the isolation amp. Also you need to make sure that the driver used to drive your power switch is also isolated.
In short, C