Family difficulty

I'm pretty sure it's the number of characters - sims and animals - you have in the household.

I see. I don't normally get a pet, and never more than one. But I'm playing Nraas rotationally and the families can get pets on their own. Imagine my surprise when I rotated in and there are all these cats! *laughs* But, I built them their own room, have plenty of litter boxes and food bowls, a bunch of beds and scratching posts. They actually take care of themselves. So really, it's not adding to the real difficulty of my family. If anything, it helps with the kids when they need social.

Disallowing adoption on your rotational caste should stop that from happening in the future. The setting applies to both human and pet adoptions. Although it sounds like you are having fun with your sims' current litter of kitties. :)

So far, it hasn't been a major problem for any of my six founding families. One family adopted an interesting dog that wants to guard everything - his food, the dining room table. And he growls at everyone EXCEPT this one kid who came over uninvited after school one day. He liked that kid and even licked his face. The funniest thing is that the dog HATES the mailman. He chases that poor guy every single day. The other day, he chased him over past the neighbor's mailbox. The poor guy actually hunched down on the other side of the mailbox waiting to see if the dog would continue to chase him. It was HILARIOUS! So yeah, I'm having a good time with the surprises. Thanks for the tip if it gets to be too much.

I didn't think they could adopt children on their own. I don't allow pregnancy so I assumed that stopped human adoptions...

ETA: So I rotated back into the family with three cats after playing my other five families and now they have a FOURTH cat! Holy moly! What has this family done? Created a cat rescue place? I guess their home is like a magnet for homeless animals!