Integrate into existing website…

I know almost nothing about coding and such, I am just an idea guy. I am working on a website for a company that has many locations internationally, and we would like to integrate something like this into our website. It would look something like this: each international arm of the company would have its own “mini-site” within the big site. These people at the international locations would be clueless as to how to do any html editing whatsoever, so what we need is an extremely easy to use interface that would allow them to (1) login, (2) post an article that doesn’t require html knowledge for simple things like italics and such, (3) would allow them to upload a picture in much the same way that they would save a document on their computer. Honestly we want something like “Blogger” but we havent been able to find it in an opensource format that we can customize to look like the rest of our site. Any help would be fantastic. Again, I know almost nothing about code, I am just the “idea guy,” but any directions you could point me in would be helpful. Thanks!