Raspberry Pi common ground with another mains connected device

[jerryk]

Yet another question with my on going old school security panel interface to raspberry pi project.  I'm getting close to sending the board out for manufacture but I may have a common ground conflict between the pi and the Napco Magnum 850 panel.  In the schematic below I am using the power from the security panel itself to step down from 12V to 5V so I can power a Sainsmart 8 -5V relay board via inputs from the raspberry pi.  As I see it the only way for this to work is to make the ground of the pi and the security panel common for the transistors to function.  Is this safe?  Or do I need to use optocouplers instead of the MMBT3904 transistors (see bottom of attached schematic)

The security panel is 12V dc that is powered by a 16vac step down transformer and then rectified on the board of the security panel.

Jerry