Can I run two force sensitive resistors on three wires?

Will my proposed design work to give independent readouts from each FSR without affecting each other?

Yes

You can replace a resistor with a potentiometer -- they are just resistors with a variable tap. Connect one end and the middle post and adjust the knob to the desired resistance.

I don't understand the last question. "Feedback loop" is not the correct term to use with this circuit.