As far as I know/understand, your Apple ID is now your "serial number" for downloaded apps. I have no definite info on how it is or will be used in iTunes, although I doubt it will be any different.
The biggest change is that with iTunes, we had to physically connect the iPod/Pad/Phone to download stuff into separate Libraries on each machine/device. With iCloud, our onliest identification remains the Apple ID but now all devices will be "connected" at the same time. At least, that's how I understand it (I was wrong wonce, however!).
I
think the only solution is to create an ID for every machine/device owner and let them do the syncing. The biggest problem then may be credit card info for some younger members. They could certainly use iTunes cards (assuming those are accepted at the Mac App Store), but my grand-daughters are
supposed to repay me on some time interval (which usually ends up being 'waived' for one reason of another.
). On the positive side, I think their knowing that I see all their purchases helps restrain their 'passion' for more 'stuff.'
I think this whole question arises because of Apple's thinking of the iCloud as a personal service, not one that is used by families. It may be what is, hopefully, the beginning of the end of the "i/Me/Mine" generation.
Plus the dependence on only the Apple ID and complete disregard for any machine/device info (<
MAC address>?!).
So, as an answer to your question, it appears that any machine that is 'attached' to your Apple ID, will get all the data/apps/songs/etc. that goes to all the other ones. If you registered your devices with Apple (which some don't!), you had a chance to use your current Apple ID or to create one...I think. But you can also create an ID or another one, as far as I know, any time you want. What I
don't know, and this is the key question, is
how that ID is connected to any device.