How to ensure an elderly parent who has caregivers coming into his home is protected from the virus right now?

You can't.
All you can do is follow the precautions set in place. Actually, CGs' may not feel comfortable coming to YOUR place.

Personally, I think this whole coronavirus thing has been blown way out of proportion--I AM taking it seriously, social distancing, staying home, washing my hands, but the news is incredibly frightening--b/c that's what the news DOES--blows stories out of the water to get ratings.

Try and calm yourself--have the necessary things AT THE DOOR when the CG comes and be sure they follow the guidelines as posted.

Being frantic and freaking out is not helping anyone.

The ideal would be just one person living with him, without going out.
People coming and going are a risk.

If it's not possible SuzanneFLORIDA posted this very useful link in another thread:
A Physician Assistant’s Guide
for anyone entering your home...
https://drive.google.com/file/d/1oV7drhW9oLiBSh3HcVTgdlHt6JHe3Xb4/view

You can’t ‘ensure protection’ from the virus for anyone, including yourself. The strongest protections (eg full white suits) are the least likely to be followed consistently. Perhaps one useful option that would actually be followed is to have a bottle of hand sanitiser just inside the front door, and get everyone who comes inside to use it on the way in. Methylated spirit works too, that’s if you can get either of them.