Was it only his parents who asked you to check his belongings? Did your friend ever ask you to do it? Or did he have any chance to tell you about bitcoin? This might be personal questions but I think before you decide how to open the wallet you should also consider what might have been the decision of your friend. If he didn’t tell anyone I doubt he wanted to leave those coins to someone, if there were any.
If he didn't tell his siblings or parents or any members of his family maybe he never though he would die so soon. Maybe he kept things to himself for privacy purpose which nobody gets to know anything about it. If the parents can get access to the coin I think it will be better than for the coin to be there without any members of the family to have access to it. His family deserves to get this coin if their is way for them to get it. Some people keeps detail of their assets to their self without allowing anyone related to them to know about it but things happens which can lead to death thst no expects.