Multiplexing AC voltages
simulate this circuit &ndash; Schematic created using CircuitLab
Figure 1. Bridge rectifiers shown as individual diodes for clarity.
In this setup the circuit is simplified by using 24 V AC coiled relays for the logic and one common voltage regulator to generate the DC if any of the AC inputs is on.
A single contact of RLY3 can be used if it's contact feeds A and B via a diode to each line.