Members should now be able to use the new GRANT feature to assign other members to a Game Journal they create. Once the initial Game Journal item is created (say just the title). A new GRANT option should appear to the right of the title.
When selected the GRANT page will give you a method to enter a user name to find the member you wish to grant permissions to your page.
Enter the member name (or partial name), once have the member name you have to select the KEEP checkbox, and select the checkbox permissions you wish to give (view, edit, delete), and lastly hit save.