Two programmers can create behaviors for actors and scenes and share in stencylforge.
And another programmer can create scenes, actors, and attach behaviors to actors and scenes from the official game.
At the end of each week copy the official game in Debug -> View -> View Folder for this Game.
And pass to other group members via Google Drive, Dropbox, etc.
Others documentations, version control, task lists, images, sounds can be shared via Google Drive Group.
And realtime communications via Skype.