Unpopular opinion, but get you and your family some cheap Chinese android boxes that will direct play the files, so that your stuff won't have to be transcoded. The biggest problem with having plex on TV's is that the majority of them can't do ATMOS, and because of that, Plex will transcode the files. Most people also don't have their TV's setup to passthrough their audio to a sound system, so they are relying on the TV itself to do the processing. The other option, is you could only encode or source versions of your movies that are compliant with what the TV's can play, ie AAC audio instead of ATMOS/TRUHD. You could also try switching to Emby, which let's you use an external player like SPMC or Kodi, which will obviously direct play the files no problem.
I am hoping that you do have a 4k capable TV and your server isn't trying to convert it down to SDR instead.