Will there be a prompt for the other party to exit the id after double authentication?

If you don't turn on dual authentication, there is nothing to show; When opened, the exit id will be displayed.

Apple mobile phone, it is best to have one account per mobile phone, or use one account at the same time. If you don't close the address book photos, they will be synchronized.

The other party's mobile phone won't receive SMS, but it will push to inform them that icloud is being used. ICloud, secure storage, easy to share. ICloud can securely store your photos, videos, documents, applications and other content, and keep them updated on your various devices. Therefore, you can access the content you want more freely and conveniently.