Ok, while I like Apple Homekit for its privacy, it definitely is a little confusing when you are managing multiple homes and lots of devices. So here are some notes:
1. As John says, if you move say an Eufy camera, there is no UI to remove them. So you have to factory reset them if you move them to another source
2. If you have multiple people using it, you have to think carefully about ownership. If you say make a camera owned by someone and a house owned by them you will lose permissions to do things like setting notifications. So normally it works better if the IT person in your extended family owns all the devices. I haven’t found a way to have levels of ownership.
3. If you have a Philips Hue Hub owned by one person, you want to change owners, it looks like you to do a factory reset by pushing the recessed pin underneath. Then the Hue application detects it as a new device. And any Hue bulbs that are around get detected as new devices. And you have to re-setup all rooms and automation. What a pain.
4. One important limitation is that you need an Apple Cloud services account to record videos. Amd there is a hard limit of only 5 cameras per paying account. So you have to juggle the cameras. Across three Homes for instance you can put 2, 2 and then one camera in.
5. In each house you need at least an HomePod mini to act as a home controller. Otherwise you won’t get sensing and so forth at $99. A 4th generation Apple TV is $149. iPads are of course more expensive. So I normally get an HomePod mini for each home.