There are several ways you can make your Sim have twins:
(NOTE: Doing both of these at the same time significantly increases the chances of having twins)
(NOTE: the treatment must be purchased before the parents woohoo, otherwise it will only work on the couples next pregnancy)
Go to the lifetime reward points bar, then click and pull up the things you can spend your points on. Give both parents the fertility treatment and you'll have twins or triplets.
To get twins, you can use the cheat "forcetwins" in the cheat console after your sim is pregnant.
It can happen by chance or you can use a cheat: SHIFT+CONTROL+C, then type forcetwins. My sims used the cheat once, then the second time they still had twins so be careful, because the guy can have a gene thing, that makes him have twins.
it was a cheat doesnt work now
No, there is no cheat code for skills on The Sims 3.
There is no real cheat for getting twins or triplets on the Sims 3 but there is a way you can increase your chances by 90%. You must have enough lifetime happiness for this although. In the lifetime rewards menu there is a reward called "Fertility Treatment" and that will increase your chances for twins or triplets. If you want twins I recommend only giving it to one of your parent sims and if you want triplets give it to them both. Note that 10% of the time this will fail, but I have only had that happen twice before. I hope this helped you!
YES THERE IS! limoparkIT DOESN'T WORK I TRIED
Yes, if there is an underscore in the cheat you have to include in otherwise it will not work.
There is no cheat for Mcdonalds in the Sims 2 or 3
There used to be a cheat but it doesn't work anymore, so no.
How can I have boy girl twins on the sims 3 pets ps3
I don't think there is because female Sims and male Sims have different clothing and it wouldn't work.
You can have children and twins on Sims 3.