How to check the available storage in the Adobe cloud storage

Hit up the following site. It's in the middle, under "Storage": https://docs.google.com/settings?hl=en

Unfortunately yes. The request to resolve this issue is pretty high in the Dropbox Votebox. Please vote for it.

You could try alternatives to Dropbox like Wuala or SpiderOak. In these applications the shared space is taken only from the user that started the sharing. The privacy features are better too.