I have an informal Sims 3 legacy challenge family that I delight in poking at every once in a while when the mood strikes me. More accurately, I guess it's not so much of a legacy challenge as it is me attempting to reach the 10th generation with a single family without getting perma-bored of that particular save (being able to move to a new town in the core game is awesome by the way). The way it usually goes with these challenges is that one heir is chosen once all of the blood related children reach adulthood. All non-heir siblings (as well as the parents sometimes) are kicked out of the house soon after
One of the problems that I have with traditional legacy style play is that after the first or so generation, it's not so much of a challenge as it is min-maxing skills through extreme levels of micro management; Which is fine if that is your cup of tea, but for me, being able to control every aspect of every sim's life not only becomes tedious but it also trivializes the challenge, given how easy it is max out skills and acquire massive wads of cash if you have control of your sims from early in their lifespan.
So for this generation I thought that it would be interesting to restrict player control to one sim. Having all other family members as NPCs adds an element of random. Unfortunately, the game as it is doesn't easily allow for this style of play. My original plan was to let my sim live out his life in bliss with his perma-girlfriend roommate and their billion children; But I hadn’t realized that when you impregnate a roommate, the baby is automatically added to your household as a playable sim upon birth. Bummer. In order to get around this issue, I had to go into the town editor, split the family by moving the wife and kids into a different lot, go back into the game, and then use the NRAAS MasterController interaction on my sim to add his wife and kids as roommates (click on household member -> Nraas -> MasterController -> Household -> Add Roommate). If you do this, make sure to do it on a fresh save just in case.
So this is Al Stewart, he is the illegitimate bastard son of Scott Stewart (5th generation legacy heir) and Vampire Wade Anthony, Scott’s favorite college professor. I used one of the NRAAS mods to breed in man babies into Scott, which kind of sort of almost broke the game. He wouldn’t STOP giving birth to man babies and perma froze on several occasions (I forgot how I fixed that problem). He is a bit... special to say the least. Story/pictures can be found here.