You want to use one or more IP cameras.
You are using a WLAN camera. Assuming the WLAN output is suitable: You still have to do wiring work. The camera needs power somehow :-). And if your WLAN name or password changes, then you have to log the camera into the WLAN again, which depending on the camera can mean that you will have to connect a laptop directly to the camera
You use a PoE-capable camera. Then you need a LAN cable running from a PoE switch or PoE adapter to the camera.
Use the existing two wires to get from your FRITZ!Box or router to the vicinity of the IP camera: Phone line or antenna cable. You will only have to cover the last few meters to the camera with the LAN cable. Power isn’t needed here. It is supplied through the two-wire LAN system.