Best way to duplicate website

Maybe you shouldnt duplicate them, but use a single installation of wordpress to manage them all in one place.

I would suggest hiring someone to do this, as some advanced skills would be required to configurate the server and build a theme that supports that.

If that isnt an option for you, you could copy the files from one server to another with an ftp client like “filezilla”. Then ex- and import the database with an mysql client like “heidisql” and adjust the settings in the wp_options table.