The invite is mailed as a link and expires in 24 hours. It works once, and only for the address it was sent to. A household holds five people, invites waiting included.
Leaving puts you in a household of your own. Your budget, accounts and linked banks come with you, and the household you leave keeps nothing of yours.
Signs out every device, this one included. A device that already holds an access token keeps it until it expires, so the cutoff takes up to 15 minutes.
Deletes the household and everything in it: accounts, transactions, categories and budgets. This cannot be undone, and signing in with the same address afterwards starts a new account. Disconnect any linked bank first.