Go to one of your movies (Star Wars Episode 1)and edit.
There is an option called Collection, this is were you can enter a name for your group eg. Star Wars.
Then when you save that, go to the other movies and when you enter the first letter of your group name it will come up with full name and enter it to all movies in that collection.
Then when you go to play a movie in plex, got down the menu list and select “By Collection” and you will have all the movies added only