^^^ What's already been said!
You realize that you will be tech support for your in-laws with this? If you have experience with IP/PoE cameras you might be OK, if not you're getting into an area of problems unless you do a LOT of research and then test each proposed camera location over a day or two at least. Even after reading and planning there's a lot more to it than you may currently realize. The road to hell is paved with good intentions.
Grand, sweeping views are fine until you need to know who did what, not just that something was done. I have a simple, rectangular, ranch house with two outbuildings. I have 20 cameras, so far, and still have some blind spots I'd like to cover. A PTZ sounds really nice but unless they plan on sitting there all day and all night watching it how will it know where to PTZ to? If it has auto tracking it will invariably be looking in the wrong direction just when it is needed the most.
If those three buildings are physically separated you need to plan on either a fiber link between them, trenching and conduit, or dedicated wireless links between them, not WiFi. The goal is to provide total electrical isolation so that damage from potential surges, lightning strikes in particular, can stay where they happen and not get to the whole system. Murphy says that will happen, trust me, and there are several reports every year on this forum of equipment being toasted by nearby, not direct, strikes. On the subject of WiFi, WiFi and surveillance cameras are mutually exclusive terms. WiFi is not reliable enough to handle the load of multiple surveillance cameras because surveillance cameras do not buffer like NetFlix movies. They constantly, without any interruption 24/7, stream full bandwidth data streams and that quickly overloads a WiFi system.