[El Gato]

Gives the impression that the unit had two commanders

There is such a thing as a Deputy Commander. Sometimes more than one. For example, III Corps has two Deputy CGs, one of those is a Cannuk on an exchange tour. Similarly 1st Cav, part of III Corps, also has a CG and two Deputy CGs.

A family friend was a deputy commander of a different Corps.

In this particular instance, I don't think the choice of words "helped command is too much of a distortion, although giving his actual position would have been more clear. Even the Command Sergeant Major is generally part of the Command Group, and could fairly to said to *help* command the outfit (boy does he/she ever.) We used different terms in the AF, but the Command Chief or Senior Enlisted Adviser was/is always a force to be reckoned with as well)

[verity]

Based on my 25 years of AD, I can tell you that there is only one person who commands a unit and has the legal authority and responsibility for that unit.

Although DCGs, XOs, and CSMs have an important leadership roles [as you suggest], command [by law as well as doctrine]is conferred upon one individual in a unit.