Simplest way to merge register and login in a single page - side by side

Currently on the login page, there is button for Registration which navigates to register page.

What would be the simplest approach ( without changing much in the code ) to merge those pages and show them side by side?

I achieved this by calling

RenderAction("Register")

inside

 Login.cshtml

file but when validation error like "Email already exists", its going to the Register view. I removed layout from Register view.

any help please?