Q:

Is it necessary to install Yoast for a website which is installed inside an existing WordPress installation folder?

I am setting up a new website inside an already installed WordPress website folder (e.g., www.example.com/newsite/). I am using the Yoast SEO plugin for my old website (www.example.com). Is it necessary to install the Yoast SEO plugin for /newsite again, and go through Google Authorization Code and Search Console too?

A:

If you are setting up a separate WordPress site (meaning no multisite) and you want to use Yoast SEO then, yes, you will have to install the plugin again. The new site has no way of using the existing copy in your old site. You also have to register it as a separate entity for Google.
I am not sure what your plan is but I would not recommend hosting a new site in a folder inside an existing domain. If you want it to rank properly, it should have its own domain. Aside from that, I would also place both sites in separate folders alongside one another instead of nesting one inside the other.

