Overwatch will help, but the only way I know to address this entirely, besides never switching active households, is to use a modded version of story progression. With the NRaas version, you can leverage its settings to prevent specified households you designate from doing certain things you don't want them to in your absence, such as adopt pets/kids, make babies, move houses, change jobs, form new romantic couplings, split up, sell all your sims' possessions for no apparent reason, etc.
Without mods, and even with the built-in progression switched off, the game will still do certain things as it feels like it such as dragoon those sims into different careers to settle a perceived imbalance of co-workers. And adopt pets, among other things, even if you've switched in and out only for a moment with the game clock paused. The way TS3 is designed, all inactive sims around town exist solely for the convenience and amusement of the sims you have active at the moment and there is little regard for the ones you wish to play rotationally.
See also: http://forums.thesims.com/en_US/discussion/comment/12998941
:)