Apple Music family share

I upgraded apple music for family plan and added my family members. Among them, some can get through easily to stream the music on app. But some have trouble to sign in at apple music though sure they were already added in my family share and they already accepted invitation. When they try to stream the music, free trial still pop up and direct to buy a plan and can't access the service I shared. What is the problem and how can we fix it???

Thank you