Using 8 half bridge load cells together
I'd do two separate 4-half-bridge load cells as in 3-wire load cells and wheatstone bridges from a bathroom scale and add their results in software or hardware.  

The issue with combing 8 half-bridge load cells into a single wheatstone bridge is that the two strain gauges in each half cell complement each other and would cancel each other out if put on the same leg of the wheatstone bridge.  If you try to wire up two wheatstone bridges in parallel directly, it will reduce the sensitivity.

You can sum the separate wheatstone bridge differences in circuit with a differential adder like "Can you sum and difference in a single op-amp?" so you could wire both separate bridges to the HX711 INA+/- through some attenuating/isolating resistors.