There are LEO sources that can provide names, current addresses and phone numbers of people who used to live at the address. So if in your example, the couple lived at a residence for 50 years, the source will show those names. If they just moved into a residence, then it is more difficult to track. If the cell phones (if they had them) are intact, we can find family names there as well. More and more people are on Facebook, which also assists in developing the next of kin.