Remove the 2 alarm wires from each PIR circuit at the panel end, place a multimeter set to continuity across the 2 wires, make sure no one is moving near the PIR to trigger it. With the PIR powered, you should get a tone or very low resistance. Now get someone to walk in front of the PIR and the meter should show high resistance or open circuit, if it doesn't then you have a fault in the wiring or PIR. If the above is ok then you need to look at the panel.