Resistive sensor reading
I'll go for the low hanging fruit here.

I suggest voltage dividers for each of the three sensors. Be sure to use stevenvh's formula for determining your other resistors for each divider:
Resistor formula for voltage dividers

In short: 

$$R = \sqrt{R_{min} * R_{max}}$$

The formula will help you obtain the greatest range in your Vout.

Then read your voltages with the ADCs in the AVR.