Unless I'm reading you incorrectly, the solution to your dilemma (though it is far from ideal) seems obvious. you say that you are stuck between hearing voices and having derealization and just hearing voices. You say that Olanzapine gives you derealization and voices, but when you are not on it, you only hear voices. Or is it that when on Olanzapine you are derealized with no voices, but when you take it you are not derealized but hear voices? If the former is the case, then it seems obvious that being off of Olanzapine is preferable. If the latter is true, then you have to decide which state is least objectionable for YOU: derealization or hearing voices, and make your decision accordingly. Of course, if both these situations are too objectionable, then perhaps you should try something different, which may require seeing a different doctor.
And please don't let your doctor or your relatives decide what is "best" for you. I know it can be difficult because we are in a position of relative powerlessness over these authority figures, but if you really want to get better and not just placate others, you need to be assertive about what you are truly feeling and what course of action is best for you.
And please don't let your doctor or your relatives decide what is "best" for you. I know it can be difficult because we are in a position of relative powerlessness over these authority figures, but if you really want to get better and not just placate others, you need to be assertive about what you are truly feeling and what course of action is best for you.