Combine rhubarb, water and 1/2 cup sugar in a medium saucepan. Bring to a boil, reduce heat and simmer until rhubarb is soft, for about 15 minutes.
Hull and quarter strawberries, then toss in a bowl with 2 Tbsp. sugar and let stand while you prepare biscuit dough.
Whisk together flour, sugar, baking powder and salt in a large bowl. In another bowl, whip cream until soft peaks form, then gently fold into flour mixture. Once dough forms a ball, knead until smooth. Cover with plastic wrap and chill for 15 minutes.
Preheat oven to 400°. Roll out dough on a lightly floured surface until it's 2/3-inch thick. Cut rounds with a 2 3/4- to 3-inch biscuit cutter; transfer to an ungreased baking sheet. Reroll scraps and cut biscuits until there are eight. Bake in middle of oven for 12 to 15 minutes. Let cool for 20 minutes on a rack.
Before serving, beat cream cheese and sugar with an electric mixer. Add heavy cream and vanilla extract and whip until thick and fluffy. Stir together rhubarb and strawberries. Split biscuits horizontally. Place bottoms on plates, and top with rhubarb and then cream mixture. Replace biscuit tops and dust with confectioners' sugar.