Sensing the higest reading from an array of NTC sensors
whichever runs the hottest will be used as feedback for thermal
  throttling and fan speed.


If you want an analogue solution use a precision rectifier circuit for each channel and tie all the outputs together. The NTC sensor that produces the highest voltage output will win the battle to imprint its voltage on the common output line. All other sensors will lose the battle and not affect the common output line.

This should work as a two input channel device: -



Whichever input is most positive will superimpose itself at Vout.