A: It can be mounted on the wall with the included screw.
A: There are 5 options available: 10, 15, 20, 25, 30 seconds.
A: They are not compatible. Only PRO add-on camera unit is able to work with the PRO monitor unit.
A: Yes. All addon camera units offer night vision.
A: Putting two camera units side by side would not cause feedback. The feedback is caused by camera unit being very close to the monitor unit and the speaker volume is set high.
A: Yes, you are able to toggle between up to 4 cameras on one monitor unit. You can only hear audio from the camera that is selected.
A: No, it's not included.
A: yes - it is for that exact purpose. Your monitor can toggle back and forth between the two cameras.