4 cups pineapple juice
5 bananas, mashed
1 (6 ounce) can frozen orange juice concentrate, thawed
1 (6 ounce) can frozen lemonade concentrate, thawed
6 cups water
4 cups white sugar
18 cups lemon-lime soda (such as 7-Up®), or as needed
Mix pineapple juice, bananas, orange juice concentrate, and lemonade concentrate in a large bowl.
Bring water to a boil in a saucepan. Dissolve sugar in the water and bring again to a boil; pour over the juice mixture and stir.
Cover bowl with plastic wrap and freeze until mixture is mushy, at least 4 hours.
Mix equal parts slush and lemon-lime soda in cocktail glasses to serve.