Freddie has a very distinct idea of Thou Shalt Not Kill, going as far as to solely target enemy buildings and artillery pieces and never the soldiers operating, and even inflicting Non-Lethal K.O. on the German troops he encounters, but when he drives a tank, you can shoot down enemy pilots, almost certainly dooming them to a fiery grave. His diary entry after defeating Baron Von Dorf in a fistfight states that he hasn't killed anyone, even after the aforementioned tank segment. Either he aimed his shots to intentionally give the pilots time to escape, or he wasn't operating the guns on the tank. Tanks need a crew of multiple men to operate, and would almost certainly require separate soldiers to drive it and man its guns.
Emile is pretty much out of uniform most of the game, with no coat, backpack, or rifle. One could assume Emile told his commander that he was okay with simply having a helmet along with his usual undershirt, boots, and pants, as he was merely the cook and occasional sapper (both roles are jobs that don't require rifles or direct killing). Frontline soldiers had greater need for the heavy clothes, especially in winter.
Karl tried to avoid fighting whenever possible, even before he was taken prisoner. Since Emile was conscripted by the French Army, Karl didn't like the idea of having to kill his own father-in-law. Under Baron Von Dorf, Karl was a Zeppelin pilot, and therefore did not need to shoot anyone while on the Zeppelin.
Anna can let Karl throw dynamite into the armored cars of French MP's chasing her, presumably killing or horrifically injuring them. Even after they threatened to bayonet her, why would she do this since she's technically on the Allied side as a Belgian medic? It'd be presumably a lot easier to explain herself and Karl, who just stole a French officer's clothes (and could easily be accused of espionage on Germany's behalf), had the French commanding officer (whose clothes Karl stole) not ordered all the military police cars to kill them, which is in itself an instance of Fridge Logic, since he could be (and is) chasing out an innocent Belgian medic. Although considering the French MP's held her at bayonet-point, it's likely that they didn't care at that point, and both sides of the war are paranoid about espionage, especially when the "spies" are escaped POW's who have seen plenty of things that are to be kept secret.
During Anna's introduction in Paris (and in some trench scenes), you can notice that even the pigeons are wearing helmets, backpacks and military purses. While this might initially feel as an slight touch of humour in portraying the notion of total war, their continued presence on the frontlines serves as a good reminder that pigeons served just as human beings and dogs, carrying messages under targeted fire, indiscriminate artillery and chemical attacks for the entire duration of the war. The war was total indeed.
