First all did your friend tell you he owns some amount of Bitcoin Before he died? or in any way tell his parents and siblings about his Bitcoin,  This way you would know where to begin with because these are things you have to be certain about so you don't end  wasting a whole lot of time seeking nothing. When this is ascertained, now this gives you the courage to do whatever you can and it will take to try to recover or get access to the wallet. His parents should also help you in checking some of his files, if by chance he wrote down his key phrases somewhere on a paper and this will make the whole process easier for you.