Combine raspberries, strawberries, cherries, 1 1/2 teaspoons lemon juice, and 1/4 cup sugar in a small saucepan. Cook over medium heat, stirring frequently, until berries release their juices, about 10 minutes. Transfer to a bowl, and refrigerate until cold.
Combine remaining 2 teaspoons lemon juice and 1/4 cup sugar with 2 cups blueberries in a small saucepan. Cook over medium heat, stirring occasionally, until berries release their juices, about 10 minutes. Transfer to a bowl. Let cool completely.
Stir in remaining 2 cups blueberries, cover, and refrigerate until cold. Whisk ice cream, milk, and vanilla in a large bowl. Spoon 1/4 cup of either fruit mixture into the bottom of a glass. Top with milk shake.
Repeat with remaining fruit and milk shake. Garnish milk shakes with fresh fruit, and serve immediately.
