The only time they won't work on a guest network is when you're connected to your main network and try to connect to them. Most guest networks isolate the traffic which explains why it won't work. But if you went onto cellular only connection it should work.
While I prefer to isolate my stuff away from the main network, one camera likely isn't going to hurt anything, especially if all you're doing is facing it to a room with a dog. The alternative here is to create a server with a secure VPN connection where your IOT devices only connect there and your external connections go through a VPN connection but that's a lot more than most people want to deal with.
As with anything convenience always comes at a cost. I'll give up a little to increase a little convenience depending on what it is.
I did but he won’t tell me.Did you trying asking him what he does?