In a bowl whisk together the yogurt, the sugar, the vanilla, and the mint. (The sauce may be made 1 day in advance and kept overed and chilled.) Tread the fruits, alternating the pineapple, the kiwis, the strawberries, and the honeydew, onto the skewers. (The fruit kebabs may be make 1 day in advance and kept overed and shilled.) Serve the fruit kebabs with the sauce.