You are reading too much into this, making assumptions.
SADP just lists the cameras in the order they respond on the network - nothing at all to do with any channel on the NVR that they are plugged in to.
Refresh SADP - and they will appear differently, depending on who gets there first in terms of tiny fractions of a second on the network.
Presumably that explains 'the camera IP addresses are always changing'. They won't be if you ignore the order in the SADP list and compare IP address against their serial number, for example.
The network settings for the PoE interface, and the LAN interface.
The bottom line is:
The IP address of, say, the camera that is plugged into NVR PoE physical port number 4 must be the same as the IP address of the NVR channel number 4.
Normally, you would simply change the camera IP address to match using SADP.
It is strange that the NVR isn't listed by SADP - normally it would appear in the SADP list as well as the cameras when the PC is connected to a spare PoE port.
Can you connect the NVR LAN port to your router easily?
As explained above - it just lists them as it finds them on the network.
SADP is happy with passwords, the cameras are all 'active', and presumably you know what you set them to. If so - best left well alone for now.
One more time - when your PC is connected to an unused NVR PoE port, set the PC IP address to 192.168.254.100
Start the browser and put
http://192.168.254.1 in the address bar and hit Enter.
Normally you'd reach the NVR web interface.
Try the same with the camera IP addresses, and confirm that you get the login prompts, and can access them with the passwords that you set.
If that was the case it would actually say so.
You need to suppress those assumptions ...
*edit* By the way - I just noticed that 2 of the cameras have the same IP address.
Unplug one for now.