I think we should begin to think like adults now. As giving ideas and then pointing the flaws out of them are not going to help the OP. And to be honest I do not think OP is going to read all the replies
Discussions like this is not only for the op but for anyone that's opening to learning because it's an opportunity to learn something. Sometimes from the subject, it could be something that you already knew but someone else might come up with a different perspective that's entirely new or help to spark up an idea in you.
But sometimes those middlemen turn up as the biggest scammers and they do not do as they are agreed. So, to avoid that, buy a Hardware wallet and give it to that middleman and tell him it is a USB which contains my last message for my kids.
I just don't like the idea of bringing a middle man into the equation. If the middle man will not claim the funds for himself, he might be bribed by one of the heirs. Making a live video and giving out clear instructions on how the Bitcoin should be shared amongst the heir and also directions on to claim the funds is actually a nice idea.