How to sync more than one calendar
1) Make sure you have added your Gmail account. Settings>Email+Accounts
2) Make sure you have selected the Calendar to sync. Click on Google and tick "Calendar"
3) Go to m.google.com/sync/ using the Internet Explorer in mobile viewon WP, and WindowsPhone should appear. If it does not appear then change the language to English.
4) After clicking on WindowsPhone, you can choose which calendars to sync (upto 25).
5) You are done. To sync the calendars now, go back to Settings>Email+Accounts, longpress Google and select synchronize.
Hope this helped. If I helped you please press Thanks.