I think I should be able to do this using castes, but is there a way to apply a caste to a bunch of sims at once? I'm doing the 100 baby thing and I want my stupid adult kids to stay in their households and not do anything all day ever, especially not die, get married, move out, or have kids. I've got dying covered with age freeze potions but they keep desperately trying to get married and move all over town so I can never find them again, and at this point I have like 8 grandkids. I've set the allow move slot thing to 0 so they should be perfectly happy staying in an 8-sim household. I created a caste called Protected that I think achieves this, but so far the only way I've found to add a caste to a sim is by clicking on the individual sim in game?

If this isn't possible, I may just have to delete them once they reach adulthood... RIP, but you're too annoying to keep around.

"Not do anything all day ever" might be too large an order to fill, I'm afraid. TS3 just doesn't work that way. But yes, you can certainly use caste level protection to disallow the individual aspects of progression that you do not want happening on these households/sims. We call this Rotational Play, and the caste you have created called Protected uses the same concept as the one I call Rotations.
http://www.nraas.net/community/Story-Pr ... e-Settings

Now then, as to how to add sims to a caste (or add a caste to sims, depends on how you look at it). Castes can be set to be Automatic so that sims belong to the caste automatically whenever and only while they meet the specified criteria. But for a protected Rotations caste, this doesn't always make sense. Castes that are Manual are only applied to sims by player command, but this can be done at the Household level and will flow down to all members of each household for as long as they continue to live there, doesn't have to be by individual sim. Does that help streamline the process a bit?