Cheesy twins
If you want twins, have one of the adults learn to make a cheesecake. Then have them try for a kid. If she gets pregnant then after she expands once, have her eat a piece of the cheesecake. This last may not always work: if the man started the woohoo, the twins will be girls, if the woman did the twins will be boys and sometimes they are both.
More tricks, tips and cheats for this game are right here - The Sims 2 cheats
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