Lots of designs inside the site and hellish architecture, which one is better?

Question

Software design

There was an old site, it needed to be completely updated. I decided to save the page addresses, so I rolled up the old pages in the database and through routing I determine and open them.
Further, there will be 6 landings inside the site, each of them has its own design different from the design of the main site, I made 6 folders in the site directory:
land1
land2
land3, etc.
In each folder, all css, js is for this landing. I decided NOT to store the landing page in the database, but to place it physically, i.e. index.php in the folder, respectively, when a request arrives, the router connects this file if the required url has arrived.
In landing pages, I wanted not to separate code and design, i.e. to do everything in one page, but some landings have 3-4 sub-landings with their design, it turns out that a primitive template engine at the level of connecting a single header and footer is still needed.
I understand that the question is strange, but can you advise me something in this situation with such a structure of the site? What is the best way to design the whole system?