Could you precise how it is possible to moderate CB Activity in order to remove spam
CB Moderators can simply just delete the post. It's completely removed from the database.
or change some wordings
There's no word filter at this time. You'd have to just edit the post, which you should be able to do as a CB Moderator.
or avoid some people ?
There's no functionality to limit who can post beyond the create access parameter.
For instance does the menu for each post removes/hides the full post for everybody or only for the viewer ? what about if the viewer is a mod ?
The hide feature is per person. It completely hides the post for the viewer who used the hide menu item.
Also can we have several moderators for a CB Activity tab within a group ? ideally that would be great to be able to add several users within a group as mods for this GJ group and be able to remove offensive message ?
GJ Groups can have as many moderators or administrators as you want. Simply join the group and promote them to moderator if desired. Group Owner, Group Moderators, and Group Administrators have moderator permissions for activity in their groups.