Here are some rules that i have made for anyone who wants to follow them...
1. To start a legacy you may only start with 1 sim. Your founder may be male or female and can be young adults, adults or for males elders.
2. NO CHEATS!!!!!!!!!!!!
3. You may have as many children a generation that you want but you can only have one living in the house for their entire life so any children that are not the heir must leave the legacy house-hold the day they become Young Adults.
4. The legacy is over when you reach Gen 10. or when your founder or heir die and no one can keep the legacy going.
5. You have to keep the graves of all the Sims living in your house when they die. So, you can make a graveyard in the backyard of the Legacy house.
6. In my legacy I have and I will only move them 1 time. Once they move the first time their is no more moving them to a new house.
7. (Attempt 1) The heir must have at least 1 trait the founder has. In my legacy the founder had the green thumb trait and that is the one all the heirs have had. You may pick the trait but, everry heir has to have it
8. (Attempt 2) Every heir must be male or female. Your choice and you do not have to do this but it is fun to do.