One issue I have not seen mentioned that might impact older travelers is medications. After a couple of decades of regularly visiting Japan, I no longer do so because age and ailments have me taking medications that are not allowed or are highly regulated in Japan. I'd suggest getting a list of your parents' important meds and then check on the Japan government website to see if any of them are listed. I inadvertently/accidentally "smuggled" in some of mine before I knew they were not permitted. Fortunately, I was not inspected when I entered back then so had no trouble. I understand the agents are being more thorough these days and someone like me might have an issue. I might not go to jail for bringing in pseudofed or enough of an opiate for a couple of weeks but they would probably take it away and that might well be just as bad..
Better to find out ahead of time than be surprised upon arrival.