Inspired by the JustnoMIL subreddit, I give you this challenge.
Begin by creating your family. You'll need an Elderly woman with an unpleasant personality. Some ideas:
dramatic, mean-spirited, hot headed, inappropriate, and family oriented
diva, mooch, dislikes children, snob, and ambitious
insane, avant garde, neurotic, over-emotional, and social butterfly
Now make her adult child and their spouse. Their traits can be whatever you wish, but make sure that the MIL's child has some trait or combination of traits that make it all worth it for the spouse. If you enjoy toddlers/children give them one or two. As a bonus make a father-in-law, he can be as pleasant or unpleasant as you wish, but MIL can do no wrong in his eyes.
Make or purchase them a house big enough for a tri-generational family to live in using whatever means you have at your disposal (cheats ok), they're all going to live together. Cheat the adult child and spouse's relationship to full green. Now think about the parent/child relationship, why have they offered to let MIL move in with them? Is it obligation? Love? Fear? Guilt? Set the mother/child relationship appropriately.
As the MIL, you win if the couple breaks up and the spouse moves out.
As the spouse, you win when the MIL dies or moves out.
As the adult child, your job is to try and keep both your mother and spouse happy at all times. It might come to pass that they must choose one. The one they don't choose must move out.
If there are children, all the adults must attempt to maintain a green relationship with them. If the grandparents' relationship gets full red, they lose and must move out.