Questions about the Legacy Challenge

My personal opinion: don't take those rules so seriously. I think everything you can do in-game without cheats, should be allowed - including all ways of warding off death, prolonging sims' life spans etc. The only "holy" rule is the one about no cheating and no mods.

Apart from that, people vary a bit - some people always make their oldest the heir, while some make the oldest of the same sex as the original family founder, some wait and choose when the kids grow up, etc. This is meant to give you a kind of challenge yet make your game more fun - if you focus too much on the rules, you will forget to have fun.