I've been playing Sims since the Sims 1 base game hit the shelves. Despite the fact that I've been playing a very looooooong time, I do remember what you are going through because I went through the same thing then, and again to some extent when Sims 2 and Sims 3 came out. So I'll help you out by giving a few observances I've made before getting to any real tips:
The Sims has always had a decent AI, and it has only improved with each new version. It's been called a "virtual doll house" and I don't take any particular issue with the analogy. It's easy enough to see the similarities. The biggest difference is that the "dolls" are smart. The Sims 3 AI is obviously the most intricate one to date: they not only have needs, they have desires. They want things, be it a piece of furniture or an interaction with a specific person (they even have a disposition for gender preference...while it's almost always "neutral," after you've played a while you'll notice that certain Sims will appear to be attracted much more to the same gender). While they always have had wants to some extent, the Sims in Sims 3 are far more motivated by them.
As such, I tend to think of my Sims as real people. Virtual people, yes...but real none the less. My responsibility as a player is to make sure that my Sims are happy, successful and safe. I am their conscience, and nothing more. I'm that little voice in their pixelated heads that says "You would do better in your professional sports career if you were a bit more athletic than you are, so get your lazy behind off the couch and hit the weights."
But even with this attitude, managing a large family can end up being a bit of work. The simplest advice is: pause and cue. The easiest way to deal with a large group of Sims is to pause the game, go to each one and assess what they need to do, and cue up the necessary actions before going on to the next one. Once they're all done, unpause and let them go at it. Try to manage it live for a bit, but when things seem to be getting out of control, pause and cue again.
If there's a Sim that doesn't really need to be doing something (i.e. they don't require immediate training or have needs that are low), you don't really need really to be all that concerned about telling them what to be doing. In those cases, just let them do whatever they want to do. Try to think of yourself as a guide rather than a puppeteer. Let them live their virtual lives while you help them to become successful at whatever they do by nudging them in the right direction when they need it.
I am of the opinion that free will is always best if set to high. If you have a bunch of actions cued up and a need starts to get critically low, they will insert an action immediately after their current action to fulfill that need, usually without dropping the rest of the cue. With free will set on high, you won't have to worry about Sims peeing on themselves or starving to death since they'll take care of these things themselves long before they get to that point.
