For isolated or atleast semi isolated inputs you have 3 main choices that spring to mind,
1: use an optocoupler with a resistor inline and a zener in parallel with both parts, so that if excess current flows it will be shunted by the zener,
this method may require a more involved calibration, and over time the parts will drift, so if you go this way try and get from the same batch, and use an extra one as a reference to compensate over time (measuring input vs output ratio)
2: Use an isolated op amp, for each input, preferably one with a built in power supply so that you do not need 16 isolated regulators $$$, this will be the most flexible approach,
3: Use op amps whos inputs can greatly exceed the supply voltage, they exist, there just harder to find, e.g. an older project used a 15V supply, and its common input range was +-110V or something along those lines, it wont be truely isolated, but for the normal 48V max for these loops as long as the supplies are referenced it shouldn't matter,