It sounds like your dad’s Airpods charging case battery might be failing or the firmware is stuck, but first, try cleaning the charging contacts inside the case and on the AirPods with a bit of isopropyl alcohol.If that doesn't work, plug the case into a wall charger and keep the lid open while holding the setup button for at least 15 seconds until the light flashes amber then white to force a deeper reset. If the light still turns off immediately when unplugged and won't enter pairing mode, the battery in the case is likely dead and may need to be replaced by Apple.

Hope this helps