Can you split the cameras to 2 different houses and apps?

You can split Nest cameras to different locations but keep in mind, cameras that are connected to different Wi-Fi networks should be added to different structures/homes to access them easily from the same Nest account. If someone is logged into your Nest account on any other phone, they will be able to view your Nest cameras, or you can add others to the specific home/structure with their email so that they also access the Nest cameras on that home/structure. You can find more details on how to share your devices in your home with others here : https://support.google.com/googlenest/answer/9155535