What should I do regarding the death of a young man by electrocution in my home, especially since his family is demanding blood money (diyya)?

Nothing is incumbent upon you, so long as you informed him of the cable's presence and warned him about it. The issue is similar to a person digging a well in his house, and then someone who entered without his permission perishes in it, or entered with his permission while the well was uncovered and he had sight. There is no liability on the owner of the well because he did not commit an aggression, and the one who entered is the one who caused his own demise. It is recommended to console the family of the deceased with some money as a voluntary donation.