I also have terrifying thoughts/fears that I would kill the people I love. I am still stuggling with this but therapy and meds really help. I do NOT think these fears will ever become a reality. There is alot of help out there for this. I would suggest seeing a professional.
I am no doctor, but it sounds very similar to my OCD. I have unwanted thoughts too and in no way do I have a desire to actually do the things it's just a tremendous fear of me being afraid I will do those things. It's like the worst possible thing I can think of and then I am afraid that is what I will do. I have to see a doctor and am on meds and it really helps me.
You need to go get professional help before your thoughts become reality. Psychotherapy and medication help alot. Also, try to speak to your parents-their are there for you-take that step-you got to get rid of this before it gets to you first.