Or just use routers with the guest WiFi feature, and set WPA2 security on it. Can't talk to your devices, only to the Internet.
I also DONT want those devices to be able to connect to the internet: I have a D-Link webcam that has (had?) some issues around being exploitable remotely via the MyDLink or whatever it‘s called service. I don’t want to have (more) devices sitting in my network that open it up from the inside.
Also I need my guests should be able to access the internet without me having to whitelist their MAC address.