Modem won't take reserved DHCP address, also want to disable public Wifi

I have new business internet service and have been tweaking the LAN setting for my local network.  I'd like to add reserved DHCP addresses for several systems but the modem is not allowing it.  There are 11 devices connected when I look at the LAN status but when I go to Connected Devices it shows none, and when I add a reserved IP it doesn't take the setting (still shows no reserved IPs in the connected devices page after adding a new one).

Also, I want to completely disable all Wifi from the device but I see the XFINITY and xfinitywifi networks oeprating despite turning off Wifi.  Is there a solution to this?

Thanks.