Internet equipment (video surveillance) in a country house
Answer
I think you need to buy a regular modem of the operator, which best catches in your house. Further, for this modem to choose a regular, stationary router. Not some small, mobile router, but a regular router. There’s just one problem here. Routers, even those that are able to distribute the Internet with 3G/4G modems, can not work with all models of modems. Perhaps you will find this article useful. There I wrote how to check the compatibility of the modem with the router.
Next, I think that the router can be placed right behind the wall where the first camera is installed. That is, the camera is outside, the router in the house just behind the wall. As close to the camera as possible. The first camera should definitely catch the signal through one wall. And if between the cameras 20 meters of open space, the second camera will be able to connect to the Wi-Fi network. Since the Internet is not wired, but through a 3G/4G modem, it is not a problem to install a router in the right place.
True, the Internet via USB modem is not the best solution for video surveillance. For the reason that it is not very stable.
I can not 100% say that everything will work as I wrote. You need to look at what and how it is set up, what signal, what router, etc. I think you understand.