Is it possible to link two iTunes accounts together?

My husband just recently got an iPhone and and iPad for Christmas. As of now his devices are registered under my iTunes account. Is it possible to link two accounts, as in his appleID and my appleID so we can share app/music content, and billing info, but also use iMessage/iCloud independently? Right now iMessage is off on his device and he can't sync with the cloud because our devices get confused and end up mirroring each other. Any help on how to separate them, but keep them linked so we don't have to buy our contents twice, but can sync separately. We use one computer (MacBook, also using my id) and he knows nothing of technology, so it's all kind of on my end to figure out, any helpful hints/suggestions are greatly appreciated.

You can use one account for the store, but each user can get their own iCloud account.