I have the exact same problem as sujichan. But there is a slight difference. I have 3 gameplays in total.(The first one) My sim parents did attend the university as well and are now back home in sunset valley. I removed 3 children from boarding school and now live at home. The other 3 children are still in boarding school. When I enter in the gameplay, first it was a blank green icon that were suppose to be the 3 children that came back from boarding school. The 3 children were acting weird. They were suppose to be sleeping in their beds in my last saved game, but then they started appearing and reappearing on the screen. They would have the (Zzzz) icon like their sleeping but then they would still be walking around like were not sleep. One of the children would be floating outside like their sleeping on the bed. The worst thing of all was I couldn't control them at all. And I even tried to reset all of them. Plus, All three of their names changed. For an example one of the girls name was suppose to be Diamond McGraw, but now its Tina Gaines. Which makes no sense at all. The sim parents are the only ones that are controllable and working.
I cleaned the university disc and thought that the disc was the problem and restarted. The second time I played that exact current game. I was able to see the 3 children this time. But they still uncontrollable and did the same weird things. So I googled. Someone said that the sims have too much in their inventory and thats why the game is not working properly. So I took a majority of items out of the sims parents inventory, it didn't work. Then, I tried what you suggest copy and replace , and replayed the game and that didn't work either. Is there a way to fix my problem? I would really appreciate it, if someone can help me solve this.