Also, how is this coordinated, and how do they prevent being shot at by their own people?
This civilians with guns are now combatants. And must "carry arms openly and respect the laws and customs of war"
Civilians do what they need to do to survive and protect their loved ones. If that means shivving a soldier in the back while pretending to be unarmed, so be it.
Having guns is way better than civilians usually get.
Anyway it probably confuses soldiers so they start shooting civilians.