IIRC, all the legs were in series.
For hookup, you will want to research Wheatstone bridge, a couple of links:
The sensors should have four wires, with two active elements and two passive.
Essentially it is two resistive dividers where one is reference and the other changes.
The output of these two dividers is treated as a differential signal going into the AD623...
The instrumentation amp gives an output that is the difference between the two inputs...