Hi there.
The best way to do this is to have each user log into Maximizer and click File>>Preferences then go to the Calendar/Hotlist tab and set their Calendar full access to Public.
Then when you log into Maximizer and go to the Calendar are you can choose the other users' calendar from the users dropdown at the top of the screen.
From here when you create a new appointment you are actually creating it in their calendar rather than creating it in yours and inviting them.