Connecting two op amp circuits each of which use dual supplies, but where the two supply voltages differ
simulate this circuit &ndash; Schematic created using CircuitLab
Figure 1. The common point of the ±5 V is simply connected to the common point of the ±12 V supply. Usually this is done  at the voltage regulators.
You may need to be careful if the output of the higher voltage op-amp is feeding the input of the lower voltage op-amp to ensure that you don't exceed the maximum input voltage.