Wash the berries, then pat dry, hull and finely chop. Transfer to a bowl and stir in 1 tsp. to 1 tbsp. sugar, depending on the sweetness of the berries. Let stand for 15 minutes to draw out the juices. Pour 2 tbsp. cold water into a small cup and sprinkle the gelatin over the water; let stand for 5 minutes.
Strain the berries over a small bowl to catch the juice. Microwave the gelatin on high for 20 seconds or until melted and hot. Stir the gelatin and 1 tbsp. corn syrup into the berry juice; fold in the berries and refrigerate for 20 minutes.
Meanwhile, peel the kiwis; puree in a food processor with 1 tbsp. sugar and the remaining 1 tbsp. corn syrup. Transfer the kiwi puree to a small bowl and refrigerate for 30 minutes.
In a chilled large bowl, using a handheld electric mixer, whip the cream and remaining 1/2 cup sugar at medium speed until stiff but not dry. Stir the vanilla into the yogurt (go ahead and mix it in the yogurt container), then gently fold the yogurt into the whipped cream.
Dollop the strawberry and kiwi mixtures on top of the yogurt-cream mixture. Drag the tip of a knife through a few times to create a marbleized effect.
Spoon the fool into 8 parfait glasses or footed small dessert bowls; refrigerate for 30 minutes. Serve with cookies.