Share one calendar - keep other calendar local

I would like to share a family calendar between my wife (Android phone) and me (iPhone) using a Google calendar.

Currently I don't store my personal calendar in the cloud but only locally on the iPhone. The family calender shall be a second calendar. Only this second calendar shall be synced through the cloud.

Now when adding the Google account at the iPhone it asks which data I want to sync (mail, notes, calendar). If I choose 'calendar' here will it also transfer my local iPhone calendar to the cloud (to Google)? Or will it only add the new Google calendar to my iPhone and sync only this calendar with my iPhone?

How can I ensure that my local iPhone calendar stays local and ONLY the family calendar gets synced?