Question: If Katherine/Silas are the ones who killed the hunter, that is Jeremy, why aren't they are cursed with the hunter's curse?
Question: When Elena and Damon were turned into rippers they were confined because they fed on vampires. Why was Lily not a threat, yet she was a ripper and never fed on vampires.
Answer: Because Lily's humanity was not turned off as Elena and Stefan's were...therefore she had some control over her actions and had a conscience whereas the other two did not at the time.
Answer: Silas did mention to Bonnie later that he was so powerful he was able to overcome Jeremy's hunter's curse in minutes.