Hello Rainer Harter,
After reviewing your post, it sounds like you want to know who you can add to Family Share. I would recommend that you read this article, it may be able to help the issue.
Start or join a family group using Family Sharing - Apple Support
You can use the steps below to add someone who already has an Apple ID to your family, as long as you're both using iOS 8 or OS X Yosemite. You can also create an Apple ID for a child and add them to your family group. When you create an account for a child, you must use a credit card as the payment method as part of providing your parental consent. After you create the child's Apple ID, you can change your payment method if you choose.
Use these steps to invite someone from your iPhone, iPad, or iPod touch:
- Go to Settings > iCloud > Family > Add Family Member.
- Enter your family member's name or email address.
- Follow the onscreen instructions.
Use these steps to invite someone from your Mac:
- Choose Apple menu > System Preferences, then click iCloud.
- Click Manage Family.
- Click +, then follow the onscreen instructions.
If your family member is with you, they can enter their Apple ID password on your device to accept the invitation. You can also send them an invitation, and they can accept from their device.
Thanks for using Apple Support Communities.
Have a nice day,
Mario