You don't necessarily need a tour operator to have a great experience in Africa. With only seven days they aren't going to get far. Seeing as how they will probably be flying into Johanusberg, they probably would get the most out of going north towards or in Krueger National Park. We stayed at a place called Londolozi. They have their own game park and pretty much assure you will see the big 5 cats. It's a 5 star all the way and a beautiful resort and a first class safari. Here's the web site. http://www.londolozi.com/
7 days there may be a bit much. So you could cap it off with a trip up to Victoria falls.