Preheat the oven to 350 degrees F (175 degrees C). Butter a 9x13-inch glass baking pan.

Place condensed milk and caramels in the top of a double boiler over simmering water on low heat. Stir frequently, scraping down the sides with a rubber spatula to avoid scorching, until melted, about 5 minutes.

Mix 1/2 cup brown sugar, apples, 1/2 cup flour, raisins, and pecans together in a bowl.

Mix remaining brown sugar, remaining flour, oats, butter, baking soda, baking powder, and salt together in a bowl until the crumbles are the size of small peas. Remove 2 cups of mixture and set aside. Press remaining crumbles firmly into the prepared baking pan; cover evenly with the apple mixture and melted caramel mixture. Top with the reserved crumble mixture, pressing lightly.

Bake in the preheated oven until light golden brown, about 35 minutes. Let cool for 15 minutes and cut into squares of desired size. Cover with plastic wrap and let cool in the refrigerator.