IOT Network Segregation from Primary Network

[csqrd]

 I just switched to FIOS from COX.  My existing network has 3 VLANs (Primary, Guest, IOT).   I was excited to see that the provided CR1000A router also supports the same network structure (Primary, Guest, IOT).   However,  I am very disappointed that the IOT network is shared with the Primary network with no isolation.  Is there a way to isolate the IOT network?  I know that the Guest network is isolated from the Primary network and I could just add my IOT devices to the Guest network but that would exposed my Guest to all of my  less than secure IOT devices including IP cameras.