No.
Would the person’s right to the money somehow depend upon:
- Your parents being, or having been married (to each other)?
-(At least) one of your parent’s written will?
- Some other document(s) signed by one (or both) of your parents?
Answers embedded.
Is the person adopted? Is the person a half or full sibling?
Just to clarify, per previously answered questions, this person is not related to me or my parents in any way, either full, half, step or adoption.
So, it looks like what we have is that at least one of your parents has named this person as a beneficiary in their will, but that person doesn’t know it. I’m unclear as to what part of this we still need to figure out, because that sounds pretty straightforward.
No. I believe that there were some initial assumptions made that were incorrect, and now everyone is off track. In the immortal words of Mark Felt, “Follow the money.”
Would a hint be available or is it impossible without giving it all away?
“Follow the money” was a hint. 
I suggest reading back through the questions and answers so far, and then asking very specific questions about your assumptions. If that doesn’t help get us back on the right track, I’ll see if I can come up with more of a hint.
I will say this: I had assumed that you (meaning everyone in the thread) would get to step 1 of the answer, which is the more obvious and direct part, quickly, and then have a lot more difficulty with step 2, which is the lateral thinking part. But you went off the rails almost immediately, and still have not gotten to step 1.
I apologize if these are repeats, but I am trying to come at this totally fresh in order to not get off track.
Does this involve real people?
Does murder mean kill or end the life of your parents?
Is this person you?
Answers embedded. I appreciate you taking this fresh approach and am hoping that it will lead in the right direction.
Is this person a child?
Is this person an adult?
Does the age of this person matter?
Aaargh! And we’re back to where we went off the rails last time, which is in focusing too much on the person, and not enough on the circumstances. Follow the money!
There is definitely something about the person that is relevant, but I think you’ll have a much better chance of solving this if you focus on trying to identify the motive.
Is the motive financial gain?
Is the motive revenge based?
Answers embedded.
Does the person know about the possibility of financial gain with your parents death?
Is the source of where the money comes from important?
Is the money the parents money currently?
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Is the money that the person would gain currently in the possession of one or both of your parents?
No.
Are the parents criminals?
Is the money to be passed down via a lawsuit or something similar?