A couple years ago I bought my parents a digital voice recorder and 128gig SD card. I asked them to spend a little time each week just talking about whatever parts of their life they wanted, and what they remember of my grandparents and great-grandparents. I don’t think they’ve done it at all. :’(
It can be really challenging to start and might be weird to speak to a recorder, if you aren't used to that kind of thing. Maybe it would be easier if you are present and they talk to you? Or maybe not, maybe they just need a reminder
Maybe start sending them your own recordings on some schedule? Not only to get them started but if you were to die before them they would have the recordings.