Firstly, The Sims 3 Supernatural is required to even get vampires and werewolves. Secondly, there is no such feature in Supernatural and thus it would be impossible to make hybrids of 2 different life forms.
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No it is not possible.
My guess is that you can't make your sim to a vampire on the sims 3.
Make sure you have at least 2 sims in a lot and when you see a vampire, make both sims friends with it and choose the one who won't be a vampire and click on the vampire with influence to... bite neck then the vampire will bite their neck and they'll become a vampire! Need COFFIN be in by 7am - 7pm or you'll burn in the sun!
They can't.
You have to get sims 3 late night to make a vampire, at this time it is only available for pc and mac. Im sorry but you can't do it on the regular sims 3 for ps3.