If your HubSpot plan allows for more than one domain, (or in other words, if the new website is located under the same HubSpot account) you can simply create your pages under the new one. If not, you should purchase a new license for each HubSpot account; that is how the HubSpot Content Hub system works. Cloning/duplicating a theme only allows you to make customizations in the theme's core files, not creating a separate website.