Duplicating Worlds without Issues

@Sophieee09 I've never tried something like duplicating a world, and I would actually be concerned to (not sure what method you used?). It would make sense that the game would be confused and bug out to do so. I played my university sims in 'off-campus' housing by having them live in homes in other worlds. If you wanted to do this in one world specifically by making changes in the game save you've been playing, you could try something like this:

Make a duplicate Game Save:

• Open the game save with the sims households you are interested in working with. Chose to save the game as a 'Save as...' and give this game save a new name. Then save and go to the 'Main Menu' > Load Game > and confirm that this new game save is in the list if game saves you can select from. 
• Enter the new game save. At this point this should be an exact copy of your other game save, with all of the same Sim households, worlds, relationships, etc. Save and go back to the Main Menu  and enter the previous game save to confirm all is normal and as you left it there. 
• Now go back to the Main Menu and re-enter your new game save (the copy of the other game save that you made) and try making your edits in this game save.

Free up homes to use for your students:

• I would recommend moving out via the 'World View' ('evict') all of the households you need to to clear out all homes you want to use for your University Sims. These households/Sims will still appear in your 'Manage Households' area in that game save, and they should still be active in the game, but until/unless you re-place them in a home you will not be able to visit them at their home or play them. 
• If you want to place them again you may want to turn on the 'free real estate' cheat or use other money cheats if their funds have been lowered by this process and you have any issue getting them back into a home they can afford.
• Now use the homes you have opened up for your university/student housing.