OK, we have 4 iTunes accounts.
1 Primary account with iTunes Match (mine)
3 accounts for individual mail and contacts (wife and kids)
They are all family members under the primary account and I have signed up for the Apple Music family trial and Apple Music works fine on my devices.
On the other devices belonging to my wife and kids when you go into Apple Music it asks you to sign up for the trial and then requires payment details rather than just enabling Apple Music...