Permissions are structured in a hierarchy. We can't have team 1 and team 2 have equal forum permissions and exclude each other from their forums. However, we can create groups that have private discussions.
We have 2 options.
1) Have general guild / class discussions open to all guild members and seperate out private discussion in the groups area.
2) Just have the forums open and have people use their discretion for posting and not post in other people's areas.