Do you need add a security group to everyone's Outlook calendar, and give that group specific rights?
Use the free PFDavAdmin tool from Microsoft. It can manage mailbox folder permissions, as well as public folder permissions.
Microsoft Exchange Server Public Folder DAV-based Administration Tool
//www.microsoft.com/downloads/details.aspx?FamilyID=635BE792-D8AD-49E3-ADA4-E2422C0AB424.
Published June 5, 2007. Last updated on June 17, 2011.