Make sure you meet the following basic requirements:
On the left side you have to subscribe to all conference rooms which you want to display on all different iPads (filtering will be done on the device itself)
Visit https://calendar.google.com/calendar/iphoneselect to select which subscribed calendars should be exported to the iPad. Do not forget to save your changes. It might take some minutes or even hours until you can see the subscribed calendars on your iPad.
Start your iPad and go to the following menu items:
Settings -> Accounts -> Add Account -> Google -> Add email adress and password of conferenceadmin
If everything is ok with your connection this is confirmed by a few hooks.
Make sure you only synchronize the calendar in the next step. All other things you don't need.
After you have successfully connected the calendar, please change to the following path in the iOS configuration:
Settings -> Calendar -> Sync
Set the value to the lowest "Events 2 Weeks Ago" and one day into the future. Depending on the calendar system and iOS versions, there may be deviations in the setting options.
When you have done that please adjust the entry "Show invitee Declines" -> off
Note that Google calendar does not support push on an iPad. Instead the events will be pulled with a delay of about 15 minutes.