Marshall is the chief of staff of the US Army, the supreme commander of the US Army and the superior of several others.

Eisenhower and MacArthur were the commanders-in-chief of the US military stationed in Europe and Asia respectively. According to the agreement between countries, they also command other allied forces in the war zone.

Bradley was the commander of Eisenhower's 12 army group, and Barton was the commander of the third army group under 12 army group.

Let's make a simple analogy:

Marshall is the general manager of the company-Eisenhower/MacArthur is the regional general manager-Bradley is the supervisor below the regional general manager-Barton is the manager.

After World War II, Marshall retired from the army, and Eisenhower also retired from the army after briefly taking over Marshall's post to prepare for politics. Bradley is his successor, serving as the army chief of staff, and MacArthur is the commander-in-chief of the US military in the Far East. Barton died in a car accident.

Only Eisenhower became president.