Mailchimp form integration with WP users

We are looking to integrate subscriber to our emailing list with WP users. Users who register to [login to view URL] should automatically also be registered as WP users. The WP username should be their email and WP password should be the one they type in the mailchimp registration form. The info between WP and mailchimp should always be in sync if users change it on WP or maichimp. At the completition of the project we need written instruction on hwo to repelicate the fix in a copy website we have.