You might have to code it yourself. WebKit is not Chrome, and a lot of Chrome has nothing to do with WebKit. They basically just use WebKit as a HTML/CSS layout engine, but not most of the rest of WebKit.
If you want multiple processes, you will have to spawn multiple processes, each of which uses WebKit to render the specified page, and then set up the necessary inter-process communication for them to work together, and basically just code it yourself. WebKit is not a magic wand you can just wave to write your code for you.