I wanted two user accounts and the admin account on the MacBook Pre (2012) to have the same iTunes library (not family sharing nor the older sharing option). Changed the path in iTunes preferences, and they all automagically had the same music etc. But the path kept getting set back to the default.
So, I moved the entire ~/Music/iTunes directory from the admin account to /Shared/Music/iTunes, put a symlink to it in all three ~/Music/iTunes, set the group sticky bit and the group ID and made it read/write for the group.
That worked for music—all accounts see any CD rips and any purchases. Works also for podcasts. But when we do an iPad sync, the available books list is different for each login account. Does iTunes Store the iBooks path as
~/Library/Containers/…? Even more weird is that the available books shown is not the same as what iBook.app shows that account as having in its library.