How to use default WP login/registration with M2 and Upfront

I want to use the default WP login/registration with M2P with Upfront Theme. So I added the following line in functions.php:

add_filter('ms_frontend_handle_registration', '__return_false');

But still when I go to "site.com/register" and click the signup button under any membership plan, it opens the front-end registration form. Also, when I click on "I already have an account" link on that page, it shows the front-end login page. Not taking me to default WP login/register page.

How can I achieve that?