You haven't been sharing one Apple ID, you have been using one Apple ID for multiple people. It's created a mess. You ought to have ONE Apple ID for each person.
Once that has been achieved one of you has to be the family organiser, probably the owner of the ID you have been using to this point. See the set up instructions here. The organiser also manages the payment for Apple's services and content so again, it makes sense for the existing ID to manage that into your new family group.
Familiarise yourself with the document What is Family Sharing? It tells you that "everyone in the family gets access to the apps, music, films, TV programmes and books that family members buy. The content automatically appears on the Purchased page in the App Store, iTunes Store, Apple Books or Apple TV app. Some items can't be shared."
*The latter refers to some apps for which the developer has told Apple that only the purchaser can use. This is not common.
You will be able to share the music from the iTunes store or the Apple Music subscription. Photos, however are a different kettle of fish. Each person's photo library will be private (although shared albums are common to all participants). Some copying and pruning of photos is in order if you want to divide your collection.
You will probably also need to buy an iCloud Storage Plan to accommodate this content.
You will have some adjustments to make and settings to tweak - Find My app for example - but it's worth it in the end.