Beat the cream and mascarpone in a medium bowl with an electric mixer until stiff peaks form, about 5 minutes. Add the instant espresso and stir gently to combine. Cover with plastic wrap and keep in the refrigerator until ready to serve.
Combine the espresso and coffee liqueur in a shallow bowl. Dip the ladyfingers into the mixture one at a time until soaked but not falling apart, just a couple of seconds. Layer in a glass in the following order: Soaked ladyfingers at the bottom, 1/4-cup-sized ice cream scoop, and whipped cream mixture. Repeat with the ladyfingers, ice cream and whipped cream. Garnish with the cacao nibs and a dusting of cocoa powder. Repeat with remaining ingredients to make 3 more sundaes.