Can I mix the camera brands and if yes, what do I have to consider?
There is no list of supported cameras, but the software features an Auto Detect feature that will automatically try to guess the name and the model of the camera. This can be done after the software is installed through the Setup settings menu. On a different view, I can't test the application because it's commercial and the information I have found above is from the User Guide available for downloading.
Read info here http://www.apeccctv.com/apecdirect/files/MegaPixelIP/SecuGuard64CHBasicUserManual_V30x_090315.pdf