Upgrading to to the Google Play Music family plan was simple and fast. Go to the settings menu inside Google Play Music and tap Refresh under your account setting.
You should see the Upgrade to family plan option pop up immediately. Tap it and follow through the steps to activate the plan. After you activate the plan, return to the settings menu and tap Manage Family. Your account settings will be displayed, Tap Manage Family Members inside the My Family card.
From there you will be able to add family members from your contacts list. I added my fiancée to my family plan although she already subscribed to her own individual plan. She cancelled her subscription inside Google Play Music’s settings menu on her device, and the app automatically subscribed her to the family plan that I previously set up without changing any of her preferences or playlists.