In a small saucepan, sprinkle 1 1/2 tsp. gelatin over cranberry juice. Let stand until softened, about 5 minutes. Stir in 1/3 cup sugar and cook over medium-high heat until steaming, 3 to 5 minutes. Evenly divide mixture among 8 glasses and chill until firmed slightly, about 70 minutes.
Meanwhile, in a small saucepan, sprinkle 1 envelope gelatin over 3/4 cup water. Let stand until softened, about 5 minutes. Stir in 1/2 cup sugar and cook over medium-high heat until steaming, 3 to 5 minutes. Chill mixture for 30 minutes or until cool but still liquid, then whisk in tangerine zest and juice. Divide between 2 bowls.
Chop segments from 4 tangerines, drain, and stir into 1 bowl of tangerine gelatin. Spoon it gently and evenly over firmed cranberry layer in glasses and chill.
When tangerine segment gelatin firms slightly, about 15 minutes, whisk yogurt into remaining tangerine gelatin (if it has firmed up, microwave until liquid but not hot). Spoon yogurt gelatin into glasses. Chill until firm, about 20 minutes. Garnish with remaining tangerine segments.
Make ahead: Chill, covered, up to 1 day.
Note: Nutritional analysis is per serving.