The rules are very simple.
First you must start of with a founder (female or male). Move them on to a plot of land. This part is optional; you can start out with a cheap house or a regular house. You may use cheats to build your house (or buy one), like I did. You can pretend the house was a gift or something like that.
Second of all, you adopt a baby. NOT a toddler or child. You can adopt up to five children, but you must have a minimum of two.
Your sim is allowed to have it’s own child, but only one. It’s your choice. This child would not be allowed to be the heir. Only the adopted ones.
15 generations should be the minimum amount to go through, but you can go higher.
Your sim can marry. But there must be atleast one generation where your sim doesn’t marry and takes care of the children themselves.
Have a photo be taken or painted of your heirs (and the founder). If you have ambitions you can do a sculpture.
The rest is up to you.
Feel free to comment down below with a link to your own adoptacy if you decide to make one. ^^