Issues with existing appointment

i work in IT and have two issues i am trying to settle for user departments -
1. If an appointment is on the executives calendar and either of his two
assistants try to add more participants (most of the appointments they added
originally) sometimes they cant add more people to the list. They can send
the new people emails, but the new folks don't show up on the list of
attendees.

2. When meetings get changed (agenda is added, the time/date, or location)
attendees aren't getting the update because the tab to notify attendees isn't
on the screen.

these issues are causing some very embarassing situatiions - any help would
be appreciated. we are using office 2003 thanks