From A-0 manual:
bombardier: nose poop gun (A-Stand oben)
radio man: remote 2 MG 131 (B-Stand)
one gunner for bottom front and rear gun (A-Stand unter, C-Stand)
rear gunner
A-0 had five crew but did not have the second MG 131 top rear gun, following versions had 6 crew.
Not optimal to have only one guy for the two bottom guns but there was not really sufficient space for two guys there.