That depends on the permission level you choose when you invite them, and the settings you configure.
Read only gives your care partner access to view your health data and chats. They cannot make any changes or interact with any modules.
Full access lets you choose exactly which modules your care partner can use. You control this with individual toggles for Chat, Health Data Management, Cross Check, Trials, and Notes. You can turn each one on or off independently. Billing, profile, and password always stay owner-only regardless of what you enable.
You can also choose whether to share your chat history with your care partner. Even if chat history is shared, any individual conversation can be made private at any time using the lock icon in the input box.
You can update your care partner's permissions at any time by going to your account menu and selecting Care Partners.
Other questions
Yes. A care partner account can be upgraded to a full CureWise account at any time if they want to use it for their own health information. They would set that up separately under their own account.