there is no way in hell the relatives of the diceased could even try and return the coins legally
it is akin trying to prove your relative had coca cola caps stash under one of the trees of your neighbour
you don't know which neighbour or tree and nobody will bother with the caps anyways
I believe now everyone can convert their bitcoin into their own currency therefore it is really valuable to have some bitcoin right now. But in this case, I think as long as you can prove that you are the owner cousin or anything related and it is still reasonable then you still can claim it. You need to discuss this to the owner of the site to withdraw everything. The important thing is their recent address and email that they used