You wouldn't need a travel router - just set up a Plex server at home. You can rip movies to a hard drive using an application called MakeMKV. You can then pre-convert the movies into an easily-downloadable format, directly in Plex (that wouldn't require transcoding each time you want to download). Next, each person can choose to download whatever movies from your library they wanted to have on their device. If you set up the server so you can access it outside your home network, then each night on the trip you can download new movies for the following day. You could also download movies directly from Netflix or Disney+ while on the trip. I don't see a reason you'd need to have the common set of movies with you in the car to stream. I did this last summer for a cross-country road trip and it worked great.