There is a tram that runs in Palm Springs, and it has a great aerial view. I think your sons would probably enjoy that. If you decide to do that, I suggest doing it in the morning before it gets too hot. (http://www.pstramway.com/)

The Moorten Botanical Gardens is a different experience than your average botanical garden. It houses an impressive collection of various Cacti and desert plants.

Elite Land Tours offers a variety of desert tours, including one of Joshua Tree. The tour I found especially interesting was the evening desert tour that provides a very different look at Palm Springs after dark. (http://www.elitelandtours.com/)

If your sons are into sports, there are some fantastic tennis and golf facilities, although it is best to get out early. The temperatures in summer get VERY high (110+ F), but it is a dry heat.