Inviting someone is a code.
You open Household. The invite code is there, twelve characters with an expiry date under them, and beside it sit QR Code and Share. On the same sofa, the QR code is enough. If your partner is at work, you send the code in a chat.
They download the app, log in with their own Google or Apple account and type in the code. And here is the whole difference: the code lets nobody in by itself. It sends a request to you. Only when you press Approve under Pending Requests are they in.