If you want complete insulation, you should use opt isolation.
V/F F/V converter(such as AD650) is useful. Changing analog signals into frequency, and send logic pulses with opt fiber.
Frequency data can be re-converted with F/V converter into analog signals.
If you can use resistor divider(it doesn't complete isolation), it's easy to use isolation amp or differential amp.
Many isolation amp don't have isolation such as 5kV, so use R divider, reduce voltage to under 1kV.
But both methods don't have good frequency responce.
It's very difficult to get good frequency responce with isolation.