Sounds like the question is how to manage multiple sims in the same household while they're on different lots.
The idea is that one sim is your priority at the moment, the one you're actively playing, and you're right that you can't be very specific about what you ask the other sims back at home to do. But you can switch back and forth. Like if you want a sim to go to the park with their friend Miki and bond, but you don't need to direct their whole conversation, you can take that sim to the park with Miki and then switch back to a sim who is at home. Then click on the icon by the sim who's at the park and click "Socialize with... Miki" and they will build their friendship without you while you play the sims at home. You can bring the sim at the park back home anytime.
