You can probably do it at the router and I think many firewall and parental suites have robust enough web filtering to give you more control and might even have a social media filter option. If all else fails modify the HOST table depending on the user rights they login with and their technical aptitude it might be sufficient.
I'd go with a DNS filtering service... refer to below list. Lots of options...quite a few modern options. Also on the list, which does get good reviews from lots of people, is Disneys "Circle" which is an appliance on your network.
DNS filtering is a blocking technology that prevents users from loading specific web content. It is based on a predefined set of rules and is imposed by a