Divide graham crackers among six dessert dishes. In a small saucepan, combine the cream, 1 cup sugar and 1 tablespoon lemon juice. Sprinkle 1 envelope of gelatin over cream mixture; let stand for 1 minute or until softened. Heat over low heat, stirring until gelatin and sugar are completely dissolved.
In a large bowl, beat cream cheese until smooth. Beat in gelatin mixture. Stir in 1 teaspoon lemon peel and vanilla. Pour into glasses over graham crackers, about 1/2 cup in each. Cover and refrigerate until firm.
In a small saucepan, combine the water, grenadine, salt and remaining sugar and lemon juice. Sprinkle remaining gelatin over water mixture; let stand for 1 minute. Heat over low heat, stirring until gelatin and sugar are completely dissolved. Pour 2 tablespoons mixture into each parfait glass. Cover and refrigerate until firm.
Refrigerate remaining grenadine mixture until syrupy, about 30 minutes. With a hand mixer, beat until frothy. Divide among glasses. Cover and refrigerate until firm. Garnish with remaining lemon peel.
