Is it possible to turn off the Two-Factor Authentication for an Apple ID?
I have more than one device linked to this Apple ID and I know the password and security questions.
To turn off Two-Factor Authentication:
Visit Manage Your Apple ID website on your computer.
Login with your AppleID / Password combo and supply the generated two-factor authentication code when prompted.
On the Account Management Screen browse to the section titled Security and click Edit.
Note: In case you are tired of entering two-factor authentication code every time you need to login via a Web-browser, there's an option to add the commonly used browser and computer as trusted browser/computer and you will no longer need to enter Two-Factor authentication code.
It is advisable to refer to the Apple Support Document, Two-factor authentication for Apple ID for the most up-to-date technical information and instructions.
You are no longer able to turn off two-factor authentication beyond two weeks from enabling the feature. Previously, this was limited to accounts created in iOS 10.3 or macOS Sierra 10.12.4 and later.
Please refer to the Apple Support Document, Two-factor authentication for Apple ID for technical details regarding Two-Factor Authentication.
Can I turn off two-factor authentication after I’ve turned it on?
If you already use two-factor authentication, you can no longer turn it off. Certain features in the latest versions of iOS and macOS require this extra level of security, which is designed to protect your information. If you recently updated your account, however, you can unenroll for a period of two weeks. Just open your enrollment confirmation email and click the link to return to your previous security settings. Keep in mind, this makes your account less secure and means that you can't use features that require a higher level of security.
What if I use two-factor authentication on a device running older software? If you use two-factor authentication with devices running older OS versions—like an Apple TV (2nd or 3rd generation)—you might be asked to add your six-digit verification code to the end of your password when signing in. Get your verification code from a trusted device running iOS 9 and later or OS X El Capitan and later, or have it sent to your trusted phone number. Then type your password followed by the six-digit verification code directly into the password field.
(from the Apple Support page Two-factor authentication for Apple ID)