I see there haven't been no replies for a while now but I have some ideas you can try...
One YA parent with 4 kids (you can try less too...) - Here's the trick, you make the house as small as possible with a lot of levels (elevator and stairs, make it even more confusing). Every child must have their bedroom on their own level. The parent's bedroom is on the top level, The house must also include at least 1 kitchen, 1 bathroom and 1 room of your choice (you can add more if you want, basement also counts as a level).
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Start with 1 parent and at least 2 children - babies. Wait 'till they both get their imaginary firend toy and age them up to toolders. Leave them with only 1 crib, and select 'sing to' or 'play with' imaginary friend before you go to free run. see to what Age you can age your Imaginary friends with only 1 crib/bed (more time for it to run around freely...)
If this topic is still gonna run I'l throw out some more ideas