How can I share apps and music purchased on one apple ID between 7 devices?
Maybe you have authorized Macs you no longer have.

Go to your account in iTunes, under Apple ID Overview you can see how many computers you have authorized and (once a year) you can deauthorize all, after that you should be able to reauthorize your Macs. (This does not affect iOS devices, as they do not count towards your 5 devices limit)