Yep, I hear ya. If you google “plex share tuner between clients” you should find old threads where this was discussed, but isn’t supported. Here is one that also has where other people encountered the problem of not recording when a non-Plex client is in use, even when there are still tuners available.
However, I can’t find that there is an actual feature request for making this change, so my suggestion is that you create one. Also, you should be able to get Live TV to work through Plex! If you want to pursue that then also open another thread regarding your Live TV issue. Make sure to include as much detail as you can - server version, client type, wired or wifi for the server and the client(s), server debug level logs…
