In my view the word "group" must be included, as the term "koncern" denotes a particular organizational structure. See e.g. N F Edström et al, Ekonomiordbok:
koncern = group [of companies] (sammanfattande beteckning på en grupp av aktiebolag som är inbördes förenade genom ett moder/dotterbolagsförhållande)
koncernledning = group management
koncernorganisation = group organization
koncernstab = group staff

Collin, English-Swedish-English Business Dictionary:
group (several companies linked together in the same organization) = koncern
group results = koncernresultat

I would think that the plural form is a trickier issue, and for this specific sentence I would translate "koncernstaber" as "group staff units." (For the singular, you could use either "group staff" or "group staff unit," depending on the context. In some instances you'd have to drop "unit," as in "group staff member.")

From links below:
Skanska strengthens focus on Health and Safety and establishes new Group Staff Unit with Neil Moore as SVP

Skanska stärker satsningen på arbetsmiljö och inrättar ny koncernstab med Neil Moore som chef