Instrumentation amps are normally used where you have a high level of interference. The IA have a high CMRR (common mode rejection ratio) where the common mode is the interfering signal on both the + and - inputs. I don't think this is the issue in your application.

Since your sensors are ratiometric, you would want the reference to the ADC fed from the same power as your sensors. That way, any change in the sensor voltage is compensated by the ADC. That's why its called 'ratiometric' - you're looking at the ratio of the value vs the reference value rather than the absolute voltage. If you're using a high resolution ADC, you have some dynamic range to play with. You can then scale/offset each sensor's value in software rather than hardware. Also, with a 24bit converter, you won't get 24bit precision, you may get 24bit resolution - in reality you'll probably only get 14 or so bits as the lower bits end up being noise. Also, a 24bit converter is usually sigma-delta - when you change the input source, you need to wait a few samples until the value settles - 4-5 are usual.


So, hopefully you won't need any op-amps!