That used to be a problem for pre 1920 planes, but in the 1920s the Synchronization gear was invented. This gear prevented the attached guns from firing if the bullet would hit the propeller. If you listen to real footage of WW2 planes firing, you can sometimes hear "hiccups" where it sounds like a bullet didnt fire, thats because it would have hit the prop, but was stopped by the sync gear.
Although, if you think this show is going to be 100% accurate to historical planes, ill say that some of these planes historically couldn't do negative-g moves (like barrel rolls or vertical climb) and yet they still pull off those maneuvers just fine in the show.
Also they built a fucking runway inside of a blimp.