The honest answer: everything, by default. A family member you’ve invited unlocks the vault with the same vault password you use, and they see the entire vault — every category, every entry, every document.
When adding or editing any entry, the “Share with” control lets you restrict that specific entry to certain people — or uncheck everyone to keep it visible only to you. Use it for the surprise gift list, the one account you’d rather keep private, the letter that isn’t ready to be read.
It’s a visibility filter, not a cryptographic wall. Everyone you invite holds the same vault password, so restricted entries are hidden by the app rather than encrypted with a different key. A technically determined family member with your vault password could get at the underlying data. That’s the deliberate trade-off of a shared family vault: it protects against outsiders cryptographically, and organizes trust inside the household.
The practical rule: invite people you trust with the whole vault. “Share with” is for tact, not for security against the people you’ve let in. If someone shouldn’t be able to see your finances at all, don’t invite them — and if trust changes later, remove their access and change your vault password.