Talking to them early and often is better than trying to convince them to make big changes in one conversation.
My parents are pretty reasonable, and were willing to postpone a flight to visit me. It helped that I'd told them in late February it was a thing to worry about, then told them again at the beginning of March that it was critical this time.
Unfortunately, it's not always enough. I can't convince my dad to skip his short business trip this week, and even though it looks like his last one for months (and he'll work from home, and my mom is retired), I'm very worried. [Edited to add: fortunately, his client cancelled the trip for him.]
I've been feeding my parents a steady stream of facts and calmly disputing hypotheses that they couldn't support with evidence ("there are lots of unreported cases", "most cases are asymptomatic", etc.). It's taken time but my father helped influence a decision to shut down schools for the whole Chicago area, citing statistics I've been supplying from the WHO.
I think the best thing you can do if they don't take it seriously is to just whittle down their resistance with facts. I tend to only pick a few to talk about in depth at a time. A fact that particularly influenced my mother was that preventing one infection today can prevent thousands over the course of just a few weeks.
As my brother pointed out to me, arguments are not won in real time. Give them information in packets and calmly deal with objections as they come up, then disengage and let them process.
People operate mostly via mimesis with a little bit of reason sprinkled on top. So it has been mostly about modifying the environment so that they will be more exposed to high status information sources saying the useful things rather than trying to pelt them with facts myself. e.g. if you show them a dashboard, people will often go back and check it themselves. If you invite them to a social media group posting updates they will find their own info and convince themselves.
Introduce changes in routines slowly over the span of a few days. Arrange cleaning supplies so that they are available but not in your face initially. Then a couple days later add to them or make them more prominent. This is much like animal behavior training. Elephant and rider. There's a famous quote that says something to the effect: 'the job of intellectuals isn't to change things now. It's to be ready with plans so that when the crisis comes and people are scrambling about for options you already have something neat and tidy to drop in their laps.' If you are gentle with the facts up front, when they do get convinced by the turning of the social tides they are much more likely to come to you as you've seeded the idea that you've already been tracking and following things. At that point if you've already bought the supplies and printed the checklists you make a nice pain free glidepath for them.
A friend of mine failed to convince her parents and ended up buying them a bunch of supplies herself.
If she manages to convince them later, the supplies will already be there, so it's definitely a good move.
For me, "Italy" sounds convincing, because it is closer to us -- I live in Europe --, geographically and culturally, than China. (Talking about China feels about as relevant as talking about Mars.)
A video from Italy, showing the crowded hospitals and soldiers on streets, would probably feel more convincing than citing numbers. (Also, this was shared on SSC.) I would only cite numbers afterwards to say something like "see, two or three weeks ago they also had only X known cases".
I would probably try convincing along the lines of: (1) if everyone will stop their social life in two weeks anyway, we might as well do it today, and (2) many people are asymptomatic or have mild symptoms, and the incubation time is several days while people already spread the virus, so by the time you know 1 person in your neighborhood to have severe symptoms, there are probably already hundred who spread the virus.
Also, when talking about the probability of death, I would add that even "non-death" can mean a lot of pain and irreversibly damaged health.
Most people are altruistic, therefore I would emphasise "you might unknowingly infect people you care about" over "you might get sick and die". (Also, gender stereotypes: men are socially conditioned to not worry about what happens to them, but they are supposed to protect their families.)
If your parents don't have Skype (or equivalent) ready, install it now.
Start buying stuff for your parents even before you have convinced them. Say "I know you don't share my worries, but knowing that you have this stuff makes me feel much better, please accept it".
A number of my friends are having difficulty conveying the seriousness of COVID-19 to their parents, or getting them to take action instead of panic. What have you found useful in convincing your parents to prep and stay home, and for bonus points, convincing their gatherings to close up?
I'm actually not a great case for answering this- my dad was born 30% prepper. But I think I could have saved a statistical life had I convinced him to convince his church to close a week earlier. And he might have been able to do that sooner had he known the technical solutions available to hold virtual church. So in addition to rousing essays and threats, please consider what tools would make parents' quarantined lives better.