Hello,
The “corporate” demos are actually just Home Pages, the internal pages come from the Porto base. You basically need to check which CSS/JS files are being added to each page you want to use, there are the “core” files, such as theme.css, theme.js, etc… but on each page there will be more specific files, by adding those you will be able to use elements from other pages.
Regarding customization, we are currently not offering services, but you can contact the team that works with Porto WordPress, they know a lot about Porto HTML and also WordPress if necessary. https://www.portotheme.com/customization/
Kind Regards.