You’ll struggle to block native mobile apps via a domain name. For example, it’s highly unlikely that the Snapchat app will be communicating with the Snapchat servers at an address that starts with ‘snapchat.com/’. It could be ‘api.snapchat.com/’, or most likely something completely different, and the app may be communicating with more than one service too, so you’ll need to know all of these addresses to be able to block it in entirety. Multiply this by the number of apps you want to block, and well… you get the picture.
Just turn off the WiFi. Or change the password.
However, that’s futile, as you can bypass your WiFi network with a 4G signal.
Which really leaves the only other feasible option… wrapping your entire house in electromagnetic mesh to create a giant Faraday cage.
That should do it.