This is a bit of a pain in the ass but making mixed reality is the best way to demo in a 2d space what it is like in virtual reality.
UploadVR has a great article here: https://uploadvr.com/make-mixed-reality-video-livestream-two-realities/ in which you can understand the basics and get started.
Here is a short shopping list for how you might get started:
$200 Sony Handycam +$150 HDMI Capture Card or a ($600) DSLR
$50 Green Screen
$20 HDMI Extension Cord
$20 two USB Extension Cord
But if you really want to get clever, add two virtual cameras! See photo below. Follow closely the instructions on how to add a virtual camera and adding a physical camera. Both are necessary and neither happens too smoothly. ENJOY!