If they are coming from Houston, they will have to go through immigration in France because they are entering the Schengen zone (most of Western Europe). So they will be landside and can go anywhere in Paris. Unfortunately, five hours really isn't enough time to go into the city. Many people like the lobby bar of the Sheraton. They could also get a day room there if they want to spend the money or if you have the points. The Sheraton is in between 2E and 2D. Other than that, there are various shops and restaurants in the airport and not a lot of great things to do nearby. Sorry.