How would someone else know this? You can't just ignore facts that don't fit your theory and still expect people to take you seriously.
How difficult would it really be to hide money/cash in the family members house and “identify” the amount/location of said funds in the fake Will to give it credibility?
Think about what you just said and whether Occam's razor might apply here.
That said, you may be very surprised at what fraudsters do in practice. Accessing bank accounts of elderly parents with or without their knowledge, accessing their electronic devices, or even creating actual forged Wills (complete with signature and notarized) is not exactly unheard of in law. Even murders made to look like suicide specifically to claim inheritance isn't just the stuff of fantasy and movies, same goes for murders made to look like accidents to claim life insurance. In fact very often it is actually a parent who murders a child for insurance money.
Here is a link that includes 21 such cases: https://www.jrcinsurancegroup.com/murder-for-life-insurance-...
In terms of bizarre things family members have done to inherit things, this sort of escapade probably wouldn't even breach the top 100.
Not a lawyer, not legal advice, you know the drill. However, the above is from my lawyer and is the policy I follow. He witnesses it AND it is notarized by a third party.