Gopro HDMI > Google Cardboard (DIY Video goggles)

I want to pipe the HDMI output from a GoPro into a split screen view that can be viewed from a phone to be put inside a google cardboard.

For reference, I'm trying to recreate top down soccer as seen in this video.

Firstly, the GoPro has wifi > phone streaming, unfortuantly however, the wifi only allows one client. But that does mean wifi video streaming is possible. So what transmitter do I need and what app can I use to see the wifi transmitted video?

If wifi streaming were viable, how would I split the video?

If it isn't what other options do I have?

Preferably, I'd like a solution that wouldn't need inteet coected wifi or mobile data (so no inteet streaming the video e.g Skype).