Webcam domain and computer independence

I want to run a dog caring business.
My home has three empty rooms and I want to use the empty rooms to keep dogs for business.
Here is my plan:
A dog owner put his dog into my empty room when he has no time to take care his dog. Each room installing one webcam and stays one dog.
A dog owner can use his computer or mobile to watch his dog in the room anytime (or particular interval each day).
As a dog owner may only leave his dog for a few days, so the dog inside a room may change frequently.
I only have one computer and a router with 4 plugs.
Here is my question:
1. Shall I need to register 3 domains for 3 rooms in my case?
2. Can I assign a user name and password to my client to filter other people to enter my webcam domain / website for privacy?
3. After a owner has taken back his dog, my order finish. Can I delete his user name of that owner and assign another user name for my new client
4. Can I use one computer to set up 3 webcams?
5. Can my webcams be still working if I turn off my computer but not switch off my modem or router.
6. Can you tell we the brand ranking of webcsms
Thanks eveybody