Sort of. You can make them very skinny by doing lots of exercise, but this also builds up their muscle. If you type in testingcheatsenabled true i into the cheat bar and hold shift down whilst clicking on your Sim and choose edit Sim in create a Sim ( this only works if you have updated your game fully) you can edit them in create a Sim. So you can make then skinny and if you give them muscle definition it looks anorexic.
You can also mess up their eating habits making them half eat a meal, or miss some, or not eat at all.
Chat with our AI personalities
Yes Vampire Sims can become pregnant in the sims 3. In fact vampirism is genetic in sims 3. eg: Sim+Vampire= Sim/Sim/Vampire/Vampire Sim+Sim=Sim Vampire+Vampire=Vampire
In the Sims 3 Island Paradise your sims can become a mermaid. In order to become a mermaid, a mermaid must give you the mermaid kelp or in life time rewards you can purchase it. Your sim must be human to become a mermaid (not a vampire, wolf, etc.)
They can only have mermaid costumes. They don't look that real you can see their feet. If you want your Sim to be a mermaid, buy the Sims 2 of download a mermaid Sim from the Internet.
no, there is no murdering in the Sims
If you mean on Sims 2 then you have to have the University expansion pack, then make a teen Sim go to college and they will turn into a young adult Sim. If it's on Sims 3, then I am not sure, sorry.