In a medium saucepan, over low to medium heat, cook the lemon juice with the raspberries and blueberries until the berries are soft. Press through a fine mesh strainer or hand food mill. Discard the pulp and seeds. Pour the berry juices back into the saucepan and heat over medium heat with the package of Jell-o and water. Boil for about 10 minutes, until it starts to thicken. Pour the mixture into a Pyrex measuring cup. Place the measuring cup into a bowl of ice cubes to cool. Set aside.
In a food processor, pulse graham crackers and Nila wafers until they are fine crumbs. Pour the crumbs into a large bowl. Mix in sugar and melted butter. Press the crumb mixture evenly into the bottom of 24 paper-lined muffin tins.
In a large bowl, using an electric hand mixer, cream together the cream cheese and sugar. Add the eggs one at a time and combine. Add in the sour cream, heavy cream, vanilla and lemon juice and mix thoroughly to combine. Scoop evenly into the 24 paper-lined muffin cups. Spoon the berry/Jell-o mixture over the mini-cheesecakes. Swirl with a toothpick.
Bake in a preheated 350 degree F oven for about 30-32 minutes. Turn the oven off and let sit in the oven for about 10 minutes. Take the muffin pan of cheesecakes out of the oven. Let cool completely. Chill for 1 hour or so before serving.