I can say that TubeArchivist is essentially single-user. Multiple accounts on a single TA instance will share the same underlying library with a ./library_dir/channel_id/video_id.ext directory structure. You could run an instance per user for individual TA libraries but, last I looked, the Jellyfin plugin doesn’t support multiple TA instances so it still wouldn’t be able to get the metadata from any instance(s) other than the one it’s configured to. It was a requested feature, on the plugin’s GitHub, but I’m not sure if it’s actively being implemented. The only workaround I can think of for now would be using a shared TA library and then manually tagging the videos in JF and using parental controls to hide them. Billy won’t see vids tagged #SusieYT, Susie has #BillyYT added to her blacklist, etc.