How to turn off Two-Factor Authentication on an iPad

She has a new iPad and an old one. She is getting pestered with sync messages and 2FA (two factor auth). I have attempted to turn off 2FA and she has a message from apple which ends:

For your security this auto message has been sent to all of the email addresses in your account.

She is worried people she has in her contacts will get a message. If so why!?

We are also fed up with 2FA requests!

I suggest she takes the old iPad off her account and just use the new one but that's not going to happen (apparently).

Would someone advise so I can get a good nights sleep?

Thanks.

[Re-Titled by Moderator]