Your group is diverse. Some want to climb Kilimanjaro before a Safari, but some prefer to skip the climb. So what should they do while the others are climbing for six days?
The non-climbers in your group could visit nearby Zanzibar island, or watch Gorillas in nearby Rwanda (though the jungle hiking can be strenuous!). Well, here's another solution for "split" groups - - while the climbers hike up Kili, the others can go on Safari in nearby Kenya - - and then all can join together for a 3 to 5 day Safari in Tanzania.
Here's a suggested schedule. Everyone flies to Moshi for an evening at the Springlands Hotel. The next day, the climbers begin their ascent of Kilimanjaro and the non-climbers head off to Kenya for Safari in Amboseli National Park, Lake Naivasha, and Masai Mara National Reserve. Five days later the two groups rejoin at the Highview Hotel to celebrate, and begin a five day Safari of Lake Manyara, Serengeti, Tarangire, and Ngorongoro Crater!
The advantage which Zara brings is flexibility to offer schedules and options which meet the desires in any group, no matter how diverse.