Factual error: The Bielski brothers go on a raid of a German post to acquire some "Ampicillin" to treat members of their refugee band who have typhus. Ampicillin is a penicillin derivative that wasn't available until the early 1960's, and in any case, typhus is properly treated with chloramphenicol or tetracycline, antibiotics of different classes from penicillin. Besides, the German didn't have penicillin of any type during World War II.
Factual error: After the final battle, Zus dismounts the tank's machine gun and puts it over his shoulder, holding it by the barrel. But the gun has been fired throughout the preceding battle (which must have just ended, as the refugees are moving as quickly as possible and wouldn't hang around for more Germans to arrive) and the barrel would be much too hot to hold.
Answer: For two reasons: one, to let him think Tuvia was going and let down Arkady's defenses; and second, Tuvia was quickly and truly debating whether or not to shoot.