Killing someone you know in a dream is an act of aggression that you envision, but should NEVER act out. You may have been hurt by these individuals unintentionally or indirectly. No matter how much you hate a person in any kind of conflict, do not act upon dreams of hurting or killing them physically because it is not worth it.
Stop for a moment to think why you are dreaming of harmful dreams, or rather nightmares because a human life cannot be bought for any money or any material in this world; and simply irreplaceable.
Talk to them or ignore them all together and move on with your life. You are wasting energy hating someone, and dreaming of inflicting harm to them that causes you to lose sleep.