With the increase in the number of Unity cards, we felt it would be prudent to clarify how Unity works in TEAMS--specifically with "shared" cards such as Fortresses, Lost Souls and occupied Sites.
Unity is read from the perspective of each player, not the team as a whole.
For example, the Sheol fortress has "Unity: Evil Characters (Share a brigade)"
If all the Evil Characters I own and control share a brigade, then I can use the ability on Sheol, even if my teammate has Evil Characters that do not match mine.
Likewise, if all the Evil Characters my teammate owns and controls share a brigade, he can also use Sheol, even if I have Evil Characters that do not match his.
Lastly, Unity can be in effect for one teammate, but not the other.