I advise the OP to consult with an attorney. Most states (read as every one that I am aware of) will treat an adopted child the same as a biological child for purposes of intestate succession statutes. In other words, it might not matter whether his "blood" relatives are on board with you taking the items or not if the adopted child is the sole heir at law. It might not be theirs to give away. And if there is a will, then obviously that would apply. Who is the administrator or executor of the estate? That is the person you need to speak with and to confirm it with the adopted children. Get everything in writing.
OK, but be aware that the statute of limitations on estate matters is often longer than it is for other matters. In my state, it is 10 years.
This is probably not your case, but I know of people who did not notify the legal system of the valuable assets after a death to 'avoid payment' against claims or taxes. When this was challenged by a family member, it became a very bad situation. You an retain a lawyer and find our your rights and risks, which is also my recommendation. The laws can vary from state.
I was able to view the coin in-hand and speak at length with shaner at the show, but will not post any details until shaner has shared more information.
Well as luck would have it... I posted a reply but didn't log in, it said it might not show up and I should log in so I did...so where is it?