I know EXACTLY what you mean - I've had the same thing happen to me. Since it doesn't help to move the families out or anything, I set about finding solutions to the problem.
Eventually I figured out that items in the house were causing it to glitch.
See, I moved in my family and placed their furniture - IT started glitching right away.
So I went into the inventory, and started putting EACH AND EVERY item into the inventory. Voila - the glitch disappeared. When I put the furniture back - it magically came back.
If you clear out the furniture room by room, you can figure out what room the glitch is in, and if you do a bit more of that you can figure out the EXACT item thats causing the problem. Understand so far?
This doesn't mean that you can't ever use the item again - usually you can just delete it and buy another one. confused
I hope this made sense, I really do. If it doesn't, PM me and I'll try and explain it again. I know what your problem is, and so this should work. Just pick up their furniture and put it into a sims inventory, and put it all back - Slowly, until you find the item causing you problems smile
Zally