Let's see if I understand the requirements correctly:
1. Normally, four rooms have completely independent control of their white lights with four independent wall switches.
2. In the alarm state, any white lights that are on go off.
3. In the alarm state, all four red lights come on regardless of the wall switch position.
If all of that is correct, then one question - do the 12 V power supplies have a low-voltage input signal for output enable, output disable, global shutdown, something like that? Many industrial supplies do, and if they are there then all of the control can be done at the low energy level. Starting with spec's two supply scheme:
4. All red lights go directly to one supply #1 without any wall switches. This supply is enabled by the house alarm signal. We'll have to work out the interface for that, but I've done a lot of these and it's pretty simple.
5. All white lights go to supply #2 through their individual wall switches. This supply is enabled/disabled by the 12 V output of the supply #1. No relays, no diodes in any power path. Both supply outputs and all lights common-grounded.
If the supplies don't have output enable signals, then one SPDT relay will be needed with an alarm control circuit (maybe just a relay coil driver), but now you're down to a single power supply.
6. The signal coming from the station that changes the lighting, "a 12v circuit that closes" - sounds more like a 12 V source that is turned on in the alarm state. Can it handle another 0.1 A of relay coil current?
ak