If you want your Sims to have anatomically correct bodies, you must leave the safety of MTS, educate yourself on the technical risks (broken saves, animation glitches, and update crashes), and venture into the adult modding scene with a clear head and a backed-up save file.
Installing the Genitals mod is relatively straightforward. Here's a step-by-step guide: Mod The Sims - Genitals mod-