To require 2-Factor Authentication (2FA) for every member of your team, you must first enroll in 2FA as the Account Owner (article).
Once completed, head over to your Account Settings.
In your Account Settings, locate your Security Settings - You'll see the option to "Require Two-Factor Authentication for your team".
The next time your users attempt to login, they will be required to enroll in 2FA.
Need to generate a Recovery Code for a member of your team? Click here.