Run Jellyfin for Offline Family Videos Viewing?

[TheDreadPirate]

I'm not sure I understand what you are requesting. Jellyfin can't be "offline" and be available to stream at the same time. If by "offline" you mean not openly accessible to the general Internet, this is the default state for Jellyfin and most routers. If the only clients you need to connect to jellyfin are on your home network, you can explicitly disable remote connections and define specific subnets to allow.