I know how to get 3 babies in one house.
You need:
?A born baby
?A baby on the way
?A mobile (under infant in home store costs 2 lp)
?One extra crib
1. Go into home store and select "move & sell"
2. Move mobile
3. Select born baby and put in another crib
4.Quickly exit store and select the crib (add new baby)
5. Pay with lp and boom 3 babies in one house.