Have a Sim with the Fertile reward trait
Use the On Ley Line lot trait
Try for a baby while the lot has the On Ley Line trait active
Increase the Sim’s pregnancy chances with the Fertility massage from a Spa Day massage table
Use the Fertile reward trait and On Ley Line together
If you have expansion packs, use the Science Baby option for a chance at multiples
Keep trying pregnancies, since twins are still random even with boosts