I have no idea why i'm asking this just now since I could've done this years ago already, but...

So I noticed that when you have more than 8 sims in your houshold, which I always have, that they're not really part of the gameworld so to speak. Meaning they won't get carpools, there are no school busses to pick them up. You also can't go to check for work in rabbitholes with them. The only thing you can do is to manually sent them to work. They also don't recieve phone calls or anything. I mean they kinda do, but the'yre always just fake calls without a conversation happening. The orginal 8 household member always work as intended. So my question would be, is that just how it is or is there a way to change that?. VIa story progression or something?

I have never noticed any of these things nor have I seen them reported here. In my overstuffed households, sims born, adopted into, or otherwise added by me are treated by the game exactly the same no matter whether they were the 1st, 2nd, or 12th sim coming on board. This includes school buses, carpools, and being pushed to work/school. If the household reaches a certain size, difficult to determine because of so many variables, then autonomy on that many sims will suffer and idle times will increase, This is where I usually slow StoryProgression down to one of its two slower speeds of progression to help take some of the stress off the game.

The one thing I'm not sure about is the phone calls, as I may never have noticed any difference if there were one.

What does "You also can't go to check for work in rabbitholes" mean? You can't send these sims out to apply for a new job?

I have always played these households with the full complement of mods designed to work with them, as discussed here. Cerainly the game stands to behave a bit differently and become more sluggish when playing extra large households, but the pattern you are describing with sims #9 and higher being that different to the game seems odd to me.

Edit: Just a thought, but how large do you let some of these households get? Beyond a certain point, I would expect the game engine to not be able to handle that many in the actively controlled household effectively no matter what settings are in place.

Interesting that it's different for you. It's like, for example, if I add a 9th sim to the houshold and make him a painter and then reach lvl 10, I can't get the fresco better paintings thingy from the city hall. The sim goes inside and comes out immediately without something popping up. Again, It's like theyre not part of the houshold. They all do behave completely normal otherwise. It's been like this for over 8 years so I always thought it would be normal. Like the game is somehow supposed to only work with max 8 sims in a houshold and after that you're on your own :p because you're operating outside of what the game's designed to do or whatever...

The average size is around 16 I'd say. It's between 14 and max 20 sims, otherwise it becomes too laggy unfortunately :p. I just can't see myself playing your usual 3 person household. I need the crazyness and stress :p. Befriending the whole town with everyone, having late night meditation sessions with 16+ sims at some lake.. Crashing parties. Having competitions of sorts between them.. those kinds of "gamey things". It's surprising to me how much fun you can still have with this game after all this time if you really go for it.

But it would be even more fun if my "extra sims" would go to work autonomously :p. Well, it is what it is I guess.

I haven't noticed this either, and I've at least played children in overstuffed households who do get the school carpool.

How are you adding these sims to your active household, and does it help to run a DebugEnabler Fix Homeworld on them afterwards? Do any opportunities at all work? You can assign one manually via MC > Basic > Opportunity.

I add them with MC - add sim. Dunno, there's nothing that indicates that something ain't as it's supposed to be. I have the game open and I can give my "extra sim" opportunties with MC. But they don't get them when I send them to rabbitholes. They just exit the buiding right away. Like they're not registered within the game in some weird way, dunno...Again, it's been like this since forever. Doesn't matter if its after a fresh, clean install, or with or without mods or whatnot.

There's another thing. I let my sims only use hoverboards to travel around. Hoverboards are kinda slowish so when it's morning and I get the message about the carpools (who don't appear for the extra sims, only for the core 8) things get really hectic because everything has to go flawlessly because if my extra sims show up at work only 1 minute too late, they don't really go to work. They just stand infront of the building for 8 hours and they don't get paid either.. If they do make it in time, they go inside and everything works normal. So yeah, as a result I end up having huge kitchens and bathrooms just to manage everyone perfectly in the morning, It goes without saying that I play with privacy off :p

I've had problems when using Add Sim, which cleared up with a DE Fix Homeworld command. So I wold suggest trying that.

That actually worked, pretty crazy. Fixed like 26 sims that way. In my defence though, I really thought this would be normal behaviour