As a hostee you can request that the members of your project be promoted to the group Project Team. This lets them see your hidden project staff forum and unlocks additional features in the board software compared to normal Members.
If you want to have someone promoted, post in this topic and an admin will take care of it.
(For those wondering: We used to have a piece of software called MasterMember that allowed hostees to do that themselves. However, MasterMember is no longer compatible with our current versions of IP.Board and we don't intend to create it again from scratch.)