Good advice Calcruzer.
Arunmit, I think rather than staying in Kingman, (which no offense to anyone, is kind of your typical, commercial, desert city), I would have them drive to Williams. The drive from Vegas to Kingman is only 2 hours away so it doesn't put them on the road all that long. The drive to Williams, (The "Gateway to the Grandcanyon") is 3 and a half hours from Vegas and puts them in the pines where it will be cooler and it's all highway driving. Williams is a small little Western town that's kind of quirky but it does have an interesting history. From Williams all they have to do is drive north an hour the following day and they'll be right at the South Rim. A website for Williams is http://www.williamschamber.com/