Crust: In medium bowl, stir together crushed cookies and brown sugar. Add butter and stir together until well coated. Press into bottom of greased 9-inch springform pan. Freeze for 1 to 2 hours or until well-chilled and set.
Cheesecake Filling: In small microwave-safe bowl, add 1/4 cup lime juice. Sprinkle gelatin over top and let stand for 5 minutes. Stir in remaining lime juice. Microwave on HIGH for 45 to 60 seconds or until hot enough to dissolve gelatin. Stir in lemon juice; let cool to room temperature.
In large bowl, using handheld electric mixer, beat cream cheese with mascarpone until light and fluffy. Beat in sweetened condensed milk, lemon zest, lime zest, vanilla and salt until smooth and blended. Beat in gelatin mixture until combined.
Spread filling over prepared crust; smooth top. Freeze for 2 to 3 hours or until firm.
Topping: In wide, shallow saucepan set over high heat, stir together 1 1/2 cups water, sugar, honey, lemon juice, lime juice and salt; bring to a boil. Cook, stirring occasionally, for 2 to 3 minutes or until sugar is dissolved.
Stir in lemon and lime slices. Reduce heat to medium-low. Cook, stirring occasionally, for 20 to 25 minutes or until fruit is tender and liquid has reduced to a slightly syrupy consistency. Using slotted spoon, transfer citrus slices to wire rack set over parchment paper–lined baking sheet.
In small bowl, add 1/4 cup water. Sprinkle gelatin over top and let stand for 5 minutes. Stir gelatin mixture into saucepan of hot citrus liquid until dissolved. Let cool to room temperature. (You should have 1 1/4 to 1 1/2 cups liquid).
Arrange citrus slices over cheesecake. Pour citrus glaze over top. Refrigerate for 2 to 4 hours or until topping is set and firm.