For tourists: how practical is bus rental when traveling between Paris, Lyon, and Marseille?

I’ve got family visiting France, and we’re trying to decide how to travel between Paris, Lyon, and Marseille. The train is fast, but tickets for a group of 15 add up quickly, and flights feel unnecessary for that distance. Has anyone here tried bus rentals for these routes? Is it practical compared to the usual trains and planes, or does it just add too much time on the road?