Ensure your version of the game matches the mod version.
Created by Deaderpool, MCCC is often considered the "master controller" of The Sims 4. It provides a massive suite of tools to manage population, outfits, and relationships. The Sims 4 Incest Mod
In some "100 Baby Challenges" or extremely long legacies, the game can sometimes lose track of distant cousins. Mods are occasionally used to fix or bypass broken relationship flags. Technical Risks and Game Stability Ensure your version of the game matches the mod version