Mix gelatin, water and triple sec in bowl; let stand 5 minutes to soften.
Combine nectar, grape juice and maple syrup in nonreactive saucepan. Bring to boiling. Remove from heat. Add gelatin mixture, zest and juice; stir to dissolve gelatin. Pour into clean bowl. Place in ice-water bath. Let cool until mixture begins to thicken and slightly set, 20 minutes.
Reconstitute powdered egg whites according to package directions, then gradually beat in sugar until stiff peaks form.
Fold diced mango and peach into gelatin mixture. Fold in egg whites. Spoon into 12 dessert glasses. Refrigerate 2 hours or until set.
To serve, top each with 1 tablespoon yogurt and 2 peach slices.