Site structure problem

Hey everyone,
i’m working on a website and came to a problem that is making me go bald.

I need to make a wordpress theme that has 3 different themes and the content for each is different. So here’s the info:

Main page (1 design, links to subpage A & B)
subpage A (gray theme with menu items A)
subpage B (white theme with menu items B)

Now to make it complicated the content structure is as followed:

Subpage A (gray theme, menu A)
– About page A
– Category (on this page it has a menu of Subpages)
– Sub categories (5-6x)
– Post of subcategory (more then 5)
– contact page

Subpage b (white theme)
– About page A (different layout than pages)
– projects category
– project names post
– gallery
-gallery category
-gallery pages
-Blog

So there’s a lot of stuff going and it kinda has to be connected. I was looking for but couldn’t find any plugins for this. But i used a function for css and if statements for specific categories. But this does’t work for pages. How would you make this work?

thanks