Combine the reserved raspberry and strawberry juices with 2/3 cup of confectioners' sugar and 2 tablespoons of cornstarch. Whisk and bring to a gentle boil, cooking until thickened, about 1-2 minutes. Chill in the refrigerator for 20 minutes.

Whip 1 cup of heavy cream until stiff peaks form, then gently fold in 3 cups of nonfat vanilla Greek yogurt and 2/3 cup of confectioners' sugar.

Break 12 ladyfingers in half and arrange half in a trifle dish. Drizzle with orange liqueur, if using. Spread one-third of the yogurt mixture over the ladyfingers.

Layer half of the mixed berries on top of the yogurt mixture, then drizzle half of the thickened berry juice over the berries.

Add another third of the yogurt mixture, followed by the remaining ladyfingers, and drizzle more orange liqueur, if desired.

Spread the last third of the yogurt mixture over the top, decorate with remaining berries, drizzle with the rest of the thickened berry juice, cover and refrigerate for at least 2 hours.