Can I make or find a device that will switch between DC inputs on a priority basis
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. A two relay solution.


If C turns on Camera C will be triggered.
If B turns on Camera C will be disabled by RLY2.
If A turns on Camera C and B will be disabled by RLY1.


RLY1 is a 2-pole relay.