Hi Thomas,
Is there any particular reason that your authors do not want their own Google+ accounts? Perhaps they do not understand the personal benefits of having an account and especially of claiming Authorship. Have you educated them about Authorship, and how it is a win-win for the publisher and writers? I'm with you, though, you shouldn't set accounts up for them unless they are on board and going to take ownership of them.
As far as claiming Authorship with your personal Google+ account, you should definitely do this -- but only on pages that contain articles or posts that you created (with your byline.) In most cases, this means you should not claim Authorship for your home page, product pages, and definitely not contact forms, terms and conditions, etc.
I'm not sure if the fact that your Google+ account is in German is relevant or not. I will definitely look into this, though. Going to ping a colleague right now. 
Cheers,
Christy
