Integration between 2 or more sites in diferent hosts.

Hello everybody,

First things first, this is not a easy task I know, but I wonder if it is possible, no mather the dificulty or the programs needed to acomplish it.

The case:
Actually I’m doing some sort of integration between a main web page almost like a page were all the client products, in this case just cars will show, like a car dealership. this is easy, and it’s all done since used some plugins and themes all mixed together to achiev my goal.

But then comes the real deal. I’ll be creating over 200 or more sites for those car dealers and so all their cars will be in their site right? Yes, but at the same time, I want to their posts to be integrated, not copied, to my site, so at the end, all dealers will have a platform wich will show all the cars in every location, where people can access to find a specific car.

This might sound confusing, but I’ll upload a image so you can understand my easily:

Click here
or paste this url
http://postimg.org/image/glhedg5ib/

So, things I need to know:

– Is it possible to alter a database in their websites who responds to a certain table in mine, so wherever they post by themselves a car, with images and information, it will automatically post in my site also?

– I’ll be using a slightly modified version of wordpress but at the same time everything works like the normal one but with some adtional features, so every page will have the same “Theme” do the site core will always be the same, but the visual CSS will difers from site to site, only in a stetic aspect.

-The site allows people to create their accounts, also their accounts have some restrictions, so All the accounts should the able to log in at their sites, but the same account will be able to log in in mine, to do the same thing but without the platform.

– Even if it is not possible to make this integration between hosts, is it possible if I use a mega host?

Thanks for your help,
Nelson Neto.