Question : SBS2008 Users receive multiple invites

I have SBS2008 (lucky me huh?)

User A has his exchange mailbox shared to all others with 'Publishing Editor'
User B has his exchange mailbox shared to all others with 'Publishing Editor'
User C has his exchange mailbox shared to all others with 'Publishing Editor'

User A has open mailboxes/calendars/contacts for User A, B, C
User B has open mailboxes/calendars/contacts for User A, B, C
User C has open mailboxes/calendars/contacts for User A, B, C

User A invites B+C to a meeting
User A receive invites for A + B + C

Desired result:

User A sends Invite, doesn't receive invites for other people, cannot respond to other peoples invites, but can read there calendars and add appointments manually if required.

Is it just a case of downgrading the share permissions?

Answer : SBS2008 Users receive multiple invites

Do they have delegate rights?

As this is why users receive invites from other users, as exchange will allow others to view/accept/decline invitations for other users.