There is four different ways you can get twins or triplets! The first way is by Trying For Baby multiple times, the second is having the pregnant sim listen to Kids music. The third is having the father or the mother have Fertility Treatment. Last but not least, you can have your pregnant sim eat apples and watermelons. 2 apples would give you twin boys, and 2 watermelons would give you twin girls.
To unlock the cheat, you must pause your game, and simultaneously press L1,R1,L2, and R2. Then, a notice will pop up and tell you to save an extra game because once you use the cheats, your challenges are stopped. If you persist, it will tell you that you can find the llama in the miscellaneous decor section in buy/build mode. Place it on your house lot and click on it to use the cheats. A few of the cheats that you can use are fill karma, unlock challenge rewards, get lifetime savings, motherlode(50,000 $), and there are some more. I hope this helped.