You have to make your NEST camera "Public," and
Blueiris will pull your video stream off internet. Yes, it sounds very stupid. I would get rid of those expensive NEST cameras and get cheap IP cameras. I bought some cheap Chinese cameras for less than $20 per piece. The image quality is not as good, but if it is just for surveillance, it is probably good enough. I can get five to ten of those cameras with the price of one NEST camera.