This is the important site here. Below some misc instructions but you need the site if you use Google calendar with some iOS devices such as iPhone or iPad.
Basic Default-calendar -setup
You can decide the default calendar in Settings more here, useful if you need to change it with different works, schools or universities for instance.
Setting up many Google Calendars to iPad under your account
Please, preview this thread here. You need nothing like CalenMob, use the default iOS -calendar and then decide which calendars to share with Apple products such as iPhone and iPad here. For some reason, Google calls it iPhone sync but in reality it handles also the iPad -calendar, perhaps also other Apple products?
Why is it enough to set up just Google -calendars?
Because you can import other calendars such as Facebook-event-calendar, more here, to Google Calendars which you can later show with your Apple products such as iPad by the above instructions. Have Fun!