Is it possible for multiple users sharing the same user account credentials to also share the same MFA key?

You can have multiple people sharing the same account (keep in mind that this is not good practice), they can share this account in their authentication app.

When onboarding, UserLock will generate both a QR code and a manual key, of which one has to be used to add the account to the application. You can take a picture of the QR code or write down the manual key to enter them in an authentication app at a later stage. It will still add the same account to the application, generating the exact same code as in the application on the other phone.

NOTE : This is only valid for the TOTP method. It is not possible for Push.