Adding multiple green screenplates into an animated 3D environment This is my first question here and I am relatively new to Blender...

I am creating a music video of band members videoed in a green screen environment to be placed on an animated 3d stage.

I will record each member separately, but I wish to be able to see all separate recordings in the one screen shot of the whole stage.  I will also have close ups of each member but I am ok with that.  

My problems are as follows and I would like to know how to fix this:

When I render a shot my render comes out the size of my green screen frame size and not the 3d camera view point of the stage.  

Q 1
Why can't I place my green screen recording onto the stage and the end result view be larger than the green screen frame size?  

Q2
How do I include the footage from two green screen recordings into the one render scene?  I am hoping that once I solve Question 1, Question 2 might be self evident.

I look forward to your assistance.
Your best bet would be to add the green screen video as a video texture on a plane object. You would need to create a black and white alpha mask clip as well to drive the transparency on the material node. This way you can have a plane object for each person in the scene and place them in the scene as needed.
Here's a test scene I just put together using this Minion green screen footage here: https://www.youtube.com/watch?v=QjN0BsUqeb4
I used blender's compositor to key out the green screen and create a black and white alpha matte video file (it's not a perfect key, but good enough for this demo):

Then I imported the green screen video use the Import Image as Plane feature. I find setting the image material to Emission works better than Diffuse in this scenario.
Then I set up the material to use the BW video file as the factor input for the Mix node that is mixing a transparent shader and the colour emission shader.

Final Output from Scene:

I should also mention that another advantage of handling the transparency via the Material as opposed to doing it in the Compositor after rendering is that you can see the character properly in the viewport when setting up your scene. This is very helpful in the pre-rendering stage for scene development.