First of all, can I offer my deepest condolences, mate. Second, if you you are sure of his "big amount" then you likely know the relevant address/es. If so, show that to his parents and tell them all necessary details so that they would be aware all things to factor in here.
By doing this, you'll be able to give them a good knowledge regarding to what your friends investments and to bring the attention of the figured that you are talking with.
Pay their close attention to fraudsters who can contact them on the matter.
This is very important so much better to give them a call to explained more deeper, it will avoid them from the hackers and scammers if they already aware of this assets.