Did you get this going? If the direct IP isn’t working for the UI it’s likely to be something in your networking setup. If you can get the UI going, but not the direct RTSP feed it’s likely the rtsp:// path is wrong - Hikvision like to move this around on different models, so Google is your friend 
You mentioned you’ve set the static route on your router. I wonder if you have the gateway correct on your cameras? Without it the traffic has no return path from the camera subnet to your LAN subnet. Whilst the NVR manages the IP address for the camera, I don’t think it sets the gateway (really dusting off the grey matter now - I’ve not owned one of these for over a year so sorry I can’t check).
I think I had to open the UI for each camera (at <NVR_IP>:<port_for_specific_camera>) and in the network settings enter the NVR IP as the Gateway address.
If that doesn’t help, can you give a bit more information on what your network IP ranges are and what the Static Route says exactly?