[kalmi10]

I found this in the FAQ:

If I want to share a calendar with my spouse, do I need to get two subscriptions? No. You can just create a normal subscription for yourself, and an "Associate" subscription for your spouse. Then share the calendar with the second account, and that's it. However, Associate accounts can't create their own calendars. So in order to have a personal calendar (that you can't see), your spouse will have to get a normal subscription too.