This isn’t so much sharing as it’s all the data associated with the same person.
More than just text messages or voicemail or call histories or two-factor authentication notifications or location or the rest are all accessible. Everything is accessible. And Apple has been busily adding more access for a while.
That ubiquitous access and control is the intent and the fundamental design of an Apple Account, too. One person per account, though some people will have more than one Apple Account.
What to do here? Set up a new Apple Account, and migrate content to it, and then set up Family Sharing.
Account creation is linked in the replies above.
Here is how to migrate your content: How to “unshare” an Apple ID - Apple Community
Here is Family Sharing: Set up Family Sharing - Apple Support