First: back up the data on that disk. Inform your parents, that the disk may fail soon and they will lose their data, if you don’t make a backup. Mirror the whole system to a fresh disk and replace the old one. Now you are still running windows, but with a lot less potential for failure. Now you can install the programs your parents would have to use on linux, to see, if they would be sufficient, or just boot a live image, like others said.