My biggest household that I'm actively playing right now is 4, but I'm really only actively playing with one of those four. I pretty much let the others do their own thing. It helps that I've been playing with aging off - there's no aging-up deadline approaching that means some particular Sim has to get their career level up soon or anything like that. Last time I played with aging on, I had it on long and one of my households had five Sims. The long lifespan made that less stressful, but I hadn't yet got the hang of finding how much I had to do with the other Sims that I wasn't actively focusing on.
I did find that my two-Teen household got a bit dull during the week, with only their evenings to do things, so they were mostly cooking and doing homework and basic needs. So now I'm playing a different household during the week, one with an active career, and my two Teens on the weekend, when I can play their free time. I've got a few households with Sims with opposite work hours or an unemployed Sim that would be good for that too.