Make file unavailable outside of local network

I have a few files that are 4K/DTS Atmos that I want to make unavailable outside of my network. My family shares my Plex server and it just cannot keep up trying to transcode these files to them. Is there a way to make files where they can only be played over a local network?

I keep 4K media in separate libraries and do not share them with remote users.

You could also give your 4K media a label, then exclude that label in sharing restrictions (Settings → Manage Library Access → user_name → Restrictions).