For us, this is perfect, but what would have been better is if you could sync multiple Photo Streams to a single iPhoto/Aperture library. That way each family member could have their own iCloud account, and you choose whose streams to sync.
Obviously this won't be suitable for everyone, but so far I can't think of a better way of doing it and it works for us.
Turn on Photosteram and 'Find My Phone' on the shared account. Turn everything else off.
Then add a second, personal iCloud account to each phone and sync everything else through that.
Share the stuff you want and not the stuff you don't.