@Beerguy - There is no such rule that you cannot file 2 or more consecutive extensions for B1/B2. I think "mangale" logic is being overly cautious. As long as you have valid reasons and proof to support your case, do it. Personally I think you have. As long as they are legally here beyond their initial entry date and all lawful extensions after that, you are just fine. They might have to explain next time while renewing their visas and/or reentry.
Just to be safe - file extensions. show health issues, pandemic and flight risks and flight ban as your reasons.
As long as extensions is pending, their presence is considered lawful. It will take few months before decision is made or you getting approval/denial. This will buy you time and they can exit when situation is favorable. If they leave before you receive extensions decision, you can always ask them to pull back the application. If you receive denial, you have to show/prove that you made effort to leave the country in a timely fashion. It doesn't have to be same or next day or within week.
hope this helps