Block adult content in network & block devices using different vpn/dns !!!

Hello,
i want to know if i can Block adult content in my network and block devices on my network from using different dns or VPN on therdevices to avoid my block rules i tried dns on router but it didnt going well , if user changed the dns for his own device or he used a VPN he can avoid the block rule !!!
Note : my network devices is PowerBeam M5 connected to normal router for wifi network.
Sorry my english languge is bad.