Family Sharing
What’s family members for sharing? Do they have to be on same phone plan? My daughter has different plan but would like to include her with family sharing.
iPhone 11
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Your daughter should be using her own individual Apple ID on her Apple devices.
Similarly, each of your other family members that you plan to invite to your Family Sharing Group (FSG), should also be using their own individual Apple IDs.
Then you, as the Family Organizer of the FSG, will invite each of the individuals to join.
It does not matter what phone plan they are using with their own individual/same carrier company.
To know more: What is Family Sharing? - Apple Support