Updating Nexus 5 from 4.4.4 to 5.0 a month late
Have you tried downloading the factory image and flashing that over a adb with a USB cable? This will normally nuke everything that was on the phone, but if you change one line in the shell script or batch file which carries out the upgrade (removing the "-w" switch) you can upgrade non-destructively. That's what I have done twice now and it works fine. 

Unless your parents are rooted, which sounds unlikely, there are no complications. If they are rooted you have to reroot after the upgrade. But that's not really complicated, and it does mean that you can have an adblock.