You wrote that your father threatened to kill you, you mention a divorce, but then you also live with them together?
If you are living with people - do they hear/get these harassing threats too? Is it just you? If friends come over, do they hear the same things? If so, then it would help your case with law enforcement. It might be even worth inviting a trusted friend to stay with you for a bit to help sort out where the threats are coming from and have another witness and source of support.
What about using your phone or a tape recorder to record the threats? This might be really important to prove your case to law enforcement. They are not likely to be able to do much of anything based on what you share here: threats in your house from an unknown source.
I would highly suggest recording the threats and playing them for others, and see if they can help you figure out the cause of them and what to do.
Is there any prescribed or in prescribed drug use occurring in the household or in your own life? Some of the threats include comments about drug use. Prescribed medications or other drugs can cause all kinds of freaky things to happen.
I highly recommend a neurological evaluation and to see a psychiatrist. Not just a general therapist. If you are concerned you have PTSD, then any good trauma therapist should be able to address what is happening and help sort it out with you.
You wrote that therapy an address the symptoms but not the cause - but that is incorrect. Therapy can and typically does address both. What does your therapist say is the cause of your symptoms or the cause of these threats? If they don't have any ideas, get another therapist! This is scary stuff to be dealing with and not something a therapist should ignore addressing the cause of this.
You could contact the police, and they could investigate as to what the cause of these harassing statement are and help you get help to deal with them.
However, I would first try to get more evidence by tape recording the threats (heck even most computers can video record and that should pick up the sound of the verbal threats being made in someone's home.) I would also really highly recommend talking to your doctor and therapist first before taking that big step as it is often a traumatizing system for people to engage. They will likely question you much more than we are here.
If these are auditory hallucinations as some suggest, they will feel as real as anything else. When someone is having auditory hallucinations, which is more common than most people think, the brain fires in a way where the sounds heard will feel as real as real life. The brain fires in the same way as it would hearing actual music or talking or etc. It could be a sign of things such as a brain tumor and combined with the confusing way you write, which would likely be atypical for you, there is much cause to talk to a doctor about this.
If there are threats coming from a person or persons, then all the more reason to get a good doctor and a good therapist to support you through the process of engaging law enforcement and moving out and getting safe and away from the person(s) making these strange and clearly scary threats.