Chaos- smashing two fractured spheres into one another

This seemingly easy setup is causing me a headache! How can I go about setting up a cinematic where I have two fractured spheres smash into each other? planets that smash into each other…I have tried making them sleeping, using kinematic but whatever I do they just go through each other with no collision. I tried parenting them to spheres, actors etc but does not work…anyone face the same issue or know of a solution greatly appreciated. Thanks