Reviving dead Sims?

First you'll need their tombstones. You can easily get these at the mausoleum with the manage the dead interaction. With the base game there is an opportunity that pops up randomly that will allow you to take a tombstone to the science center and bring them back as playable ghosts. Alternately you can just place the tombstones on you home lot and they'll 'pop up' periodically at night (particularly when the full moon is out if you have Supernatural). With Supernatural you can have a witch sim who has mastered the magic skill raise them as zombies (then, if desired use alchemy to cure them of being zombies). You can also use the philosopher's stone to bind their ghosts to your household(making them playable ghosts)and have them eat the ambrosia that way.