Hmm Odd. Never had my other sims run off when I go travelling with one or two of my household however with that said - you may want to look into the Mod Life Manager (look on DWP), you can essentially tell the sim to ignore social interactions and focus only on say cleaning or nursing babies, etc. That might be one way.
I dont know if you got Sugar Dating App and they run off when someone calls em, that might be something to look into, if you got any mods that add events for them to do on their own.
Essentially look into the autonomy options that are out there - that might be your best bet.
Hope that helps and if I'm completely off the mark, let me know