The short answer
Family members cannot browse your library through Family Sharing. They can see photos you put in the iCloud Shared Photo Library, photos you add to a Shared Album, and everything on any device that is signed in to your own Apple Account. Photos in a Kryptis vault are in none of those places.
Three different things
Family Sharing. Shares an iCloud storage plan, App Store purchases, subscriptions and optionally location. It does not share your Photos library.
iCloud Shared Photo Library. Introduced in iOS 16. You and up to five people share one library. Photos you move into it, or that are added automatically by the rules you set, are visible and editable by everyone in it. Photos in your personal library stay yours.
Shared Albums. Specific albums you invite people to. Only what you add.
The one that catches people
A family iPad, an old phone, or a Mac signed in to your Apple Account with iCloud Photos on is your library, all of it. The Hidden album is on that device too, behind the device's own Face ID or passcode, which a family member may well know. More on what the Hidden album does not protect.
What to check
- Settings, your name, Family Sharing: see what is shared. Photos is not on the list.
- Settings, your name, iCloud, Photos: look for Shared Library. If it is on, review the automatic sharing rules.
- Settings, your name, then scroll to the device list. Any device you do not hold is a device with your library on it.
Keeping photos out of all of it
Photos in Kryptis are not in the Photos library, so they do not sync, do not join a Shared Library, and are not on any other device unless you restore a backup there. The vault opens with its own passcode, not the device's. Encryption on the phone.
