To Move A Sim Into a Different Neighborhood
Play with the family in their original neighborhood. Make sure the save html option is on. Exit to the neighborhood screen. Click on "view web pages" in the upper right corner. Close the browser window that pops up and exit the Sims game. Open c:\program files\maxis\the sims\Userdata(or Userdata 2,3,4,5,6,7,or 8)\Export. Locate the family name (you can make it easier by sorting by name or date). Copy both ".pub" and ".FAM" files for the family and paste into c:\program files\maxis\the sims\userdata\import. the family and its house will be available for import into whatever neighborhood you like the next time the game is loaded. If you wish to have only one family then use cut--but I don't recommend this until you're sure it works.

Help With Guinea Pig Disease
Buy the Guinea Pig portrait. If that doesn't work, try getting the chemistry set and making a white potion. Or use the move_objects cheat to delete them and then bring them back by double-clicking on the portrait below. Or evict them and move them back in. Or never get a pet Guinea Pig or a pet that was made from it. An alternate Guinea Pig portrait is available from The Well-Dressed Sim.
Help With Sickness
If your sim is just sick, try giving him/her plenty of rest and coffee. Or try eviction, the white potion, or the cheat like above.