Setting up a flat panorama with 4 cameras

I'm trying to create a scene to be used in an event. The task is to create a summer-view that is then projected onto a wall in the main venue. The system at the venue consists of a single computer and four FullHD projectors.

How do I go forward in making this? I've already set up 4 cameras in the scene, with each targeting displays 1 to 4. e.g. Camera 1 sends image to display 1. I've also manually positioned the cameras to produce almost seamless image of the forest about 100 units away. I use Azure[Sky] as a sky projected on the inside of a sky-sphere. I cannot use the normal skybox because it renders per camera.

The largest problem here is that while the forest around 50m(or units) in front of the cameras is seamless, the sky isn't. I'm getting 4 individual sunsets and the clouds do not appear seamlessly between the cameras. Same goes for anything that is in the "seam" in the foreground.