Need a protection diode if only connected by common ground?
I've modded your circuit with notes. I'm sure the mosfet being upside down is a circuit diagram mistake but unless you put pull-down resistors on the gates to 0V they'll be triggering on any amount of EMI local to the circuit. I'd use 10kohms.

I'd also put diodes across the loads being switched by normal switches too, if only to elongate the switch's life and reduce EMI.