Okay. They can’t be killed by conventional means like a gun or a knife. You’re going to need something more…supernatural in nature. I’m assuming that you are human, so some of the weapons I used won’t be available to you. Instead, try looking into the occult, specifically protective and warding spells and rituals. If you can apply the right ward to a weapon, that should be able to kill them, or at least dispel them for a while. Hopefully that helps you. These things have been allowed to roam unchecked for too long. I wish you luck. You’ll need it.