I've had twins in my other saves in the hospital. I have the parents woohoo twice as part of a ritual that tends to work from Sims 2. The funny thing in my legacy save I can't get twins or baby girls, which is a pain for progressing in my matriarch strict rules legacy game. But in the other games twins pop up all the time, because I use the fertility treatment and on ley line lot trait.
The thing that's difficult for me to get is triplets. I've had only one set of triplets and one set of quads from the Villareal father with his mistress. The kids all looked like him with a big nose except one girl looked like Luna with black hair. The triplets and quads just happened without using any rewards. The mother lived alone and I'm thinking that increased the odds for multiples.
