You can have seperate calendars, but overlay them so they are viewed at the same time in SharePoint 2013.
You can overlay either Exchange or SharePoint calendars using this function. I have attached a link that describes using Calendar Overlays in more detail.
http://office.microsoft.com/en-us/sharepoint-foundation-help/overlay-a-sharepoint-calendar-with-a-calendar-from-exchange-or-sharepoint-HA101777171.aspx