Family Ideas?

Start with your single sim, as above and send them travelling if you want to but have them actually build their family in-game. Don't have too many children and have one of those children pegged for the legacy, basically to go on and do the same thing. Find and build a family. I rarely build families. I always start with a single sim. Personally I find this fun because otherwise, everything is pretty much done, you have so many sims that you can't really connect with any of them as a character and I personally find a lot of sims difficult to care for.

Also, make sure freewill is on high, that way after your sim has had their family, you can concentrate on your legacy sim.

Other tips, either randomise or mix traits, try all careers, give your sims a backstory, get a pet, give them hobbies and quirks and you should end up with sims that you actually care about for more than a few days. I imagine that if I just started with a fully made family and no back story, I'd have difficulty caring and would just abandon the family too after a few days. So my suggestion would be first and foremost, make yourself actually care about the game you're playing and that will make any scenario fun.