Stop kids adding new devices at night

[Parent1]

We have set up sky WiFi max to pause devices internet access at night. We created a group contains all the connected devices. The issue we are having is our teenagers just add new devices. There are able to rename devices to add them again . For example we now have 15 different named x-boxes that have been linked to the Wi-Fi. How can either prevent them from being able to add any new additional devices or block any devices from using the internet at night ? 

[Chrisee]

@Parent1 the parental control system that is totally kid proof doesn't exist and as your kids have found spoofing a mac address gets round Sky's system. Most every system can be defeated by a tech savvy teen if your's aren't knowledgable themselves they will haveca friend who is.

[Parent1]

Is there a way of blocking the internet without switching the router off